Optical functional film, retardation film, composition for forming optical functional layer and producing method of optical functional film

ABSTRACT

An optical functional film which exhibits excellent optical characteristics without using an alignment film, and having the excellent adhesion property between layers. The optical functional film includes: a substrate having a property as an optically negative C-plate, and an optical functional layer formed on the substrate and having a rodlike compound. The optical functional layer is formed directly on the substrate, and the rodlike compound forms a random homogeneous alignment in the optical functional layer.

TECHNICAL FIELD

The present invention relates to an optical functional film to be usedin a liquid crystal display, etc. and a producing method of the same.More particularly, the invention relates to an optical functional filmwhich has a novel alignment form of random homogeneous alignment, andexhibits an excellent adhesion property between an optical functionallayer and a substrate and excellent optical characteristics.

BACKGROUND ART

Owing to the characteristics of such as power saving, lightweight andthin shape, the liquid crystal displays have recently been spread at ahigh rate instead of the conventional CRT displays. As a common liquidcrystal displays, one comprising incident side polarizing plate 102A, anoutput side polarizing plate 102E and a liquid crystal cell 104 as shownin FIG. 6 can be presented. The polarizing plates 102A and 102B areprovided for selectively transmitting only a linear polarization (shownschematically by the arrow in the figure) having an oscillation plane ina predetermined oscillation direction, disposed in a crossed Nicol statewith their oscillation directions perpendicular with each other.Moreover, the liquid crystal cell 104 includes a large number of cellscorresponding to the pixels and is disposed between the polarizingplates 102A and 102B.

As the liquid crystal displays, those of various systems have been putinto practice according to the alignment form of the liquid crystalmolecules comprising the liquid crystal cell. Recently, those of the VA(vertical alignment) system are the mainstream. The liquid crystaldisplays of the VA system are widely used mainly for the liquid crystaltelevisions.

As to the liquid crystal cells used for the above-mentioned liquidcrystal displays of the VA system, since the liquid crystal moleculesare aligned vertically, the liquid crystal cells as a whole has theoptical characteristics to function as a positive C-plate. For example,if the liquid crystal cell 104 of the liquid crystal display 100 shownin FIG. 6 has such optical characteristics, a linear polarizationtransmitted the incident side polarizing plate 102A passes through acell portion in the non driven state out of the liquid crystal cell 104without the phase shift so as to be blocked by the output sidepolarizing plate 102B. On the other hand, at the time of passing througha cell portion in the driven state out of the liquid crystal cell 104,the linear polarization has the phase shift so that a light beamaccording to the phase shift amount is transmitted and outputted fromthe output side polarizing plate 102B. Therefore, by optionallycontrolling the driving voltage of the liquid crystal cell 104 per cell,a desired image can be displayed on the output side polarizing plate102B side. The liquid crystal display 100 is not limited to those havingthe light transmission and shielding embodiment mentioned above. Aliquid crystal display provided such that a light beam outputted from acell portion in the non driven state out of the liquid crystal cell 104is outputted after transmitting through the output side polarizing plate102B and a light beam outputted from a cell portion in the driven stateis shielded by the output side polarizing plate 102B is also proposed.

Considering the case with a linear polarization transmitting a cellportion in the non driven state out of the VA system liquid crystal cell104 mentioned above, since the liquid crystal cell 104 has birefringenceand has different refractive indexes between a thickness direction andan plane direction, although a light beam inputted along the normal lineof the liquid crystal cell 104 out of the linear polarizationtransmitted the incident side polarizing plate 102A is transmittedwithout the phase shift, a light beam incident in the direction inclinedwith respect to the normal line of the liquid crystal cell 104 out ofthe linear polarization transmitted the incident side polarizing plate102A becomes an elliptical polarization due to the retardation generatedat the time of transmitting the liquid crystal cell 104. This phenomenonis caused because the liquid crystal molecules aligned vertically in theliquid crystal cell 104 functions as a positive C-plate. The size of theretardation generated to the light beam transmitted the liquid crystalcell 104 (transmitted light beam) is influenced also by such as thebirefringence value of the liquid crystal molecules sealed inside theliquid crystal cell 104, the liquid crystal cell 104 thickness, or thewavelength of the transmitted light beam.

Due to the above-mentioned phenomenon, even in the case with a cell inthe liquid crystal cell 104 is in the non driven state and a linearpolarization should be transmitted as it is so as to be shielded by theoutput side polarizing plate 102B, a part of the light beam outputted inthe direction inclined with respect to the normal line of the liquidcrystal cell 104 is leaked from the output side polarizing plate 102B.Therefore, according to the conventional liquid crystal display 100 asmentioned above, a problem of the deterioration of the display qualityof an image observed from the direction inclined with respect to thenormal line of the liquid crystal cell 104 compared with an imageobserved from the front side (viewing angle dependency problem) has beenpresent.

In order to remedy the problem of the viewing angle dependency in theconventional liquid crystal display 100 as mentioned above, a variety oftechniques have been developed up to now, and a typical one thereof is amethod of using an optical functional film. In the method of using theoptical functional film, the problem of the viewing anglecharacteristics is remedied by disposing an optical functional film 60having given optical characteristics between a liquid crystal cell 104and a polarizing plate 102B as shown in FIG. 6. As the opticalfunctional film used to remedy such a problem of the viewing anglecharacteristics, retardation films exhibiting a refractive indexanisotropic property have been used, and have come to be widely used asa means for remedying the viewing angle dependency in theabove-mentioned liquid crystal displays.

Heretofore, the above retardation film generally has the construction inwhich as shown in FIG. 7, an alignment layer 72 is provided on anarbitrary transparent substrate 71 and a retardation layer 73 havingliquid crystal molecules is formed on the alignment layer 72, so thatthe liquid crystal molecules are aligned by an alignment controllingpower of the alignment film and thereby a desired refractive indexanisotropic property is exhibited. As such retardation films, asdisclosed in Patent document 1 or 2, for example, there are retardationfilms in which a retardation layer having a molecular structure withcholesteric pattern regularity (a retardation film exhibitingbirefringence) is formed on a substrate having an alignment layer.Meanwhile, Patent document 3 discloses a retardation film in which aretardation layer composed of a discoid compound (a retardation layerexhibiting birefringence) is formed on a substrate having an alignmentlayer.

The above retardation films are useful in that the problem of theviewing angle dependency of the liquid crystal display can be largelyremedied by appropriately designing the refractive index anisotropicproperty to offset the retardancy caused in the liquid crystal cell ofthe liquid crystal display. However, since the conventional retardationfilm took, as an indispensable component, the alignment layer foraligning the above liquid crystal molecules, there was a problem in theadhesion property between the alignment layer and the retardation layer.

In order to solve this problem, for example, Patent document 4 proposesthat the adhesion property is improved by thermally treating liquidcrystals and the alignment layer. According to this method, however,when the substrate is not a glass substrate but a substrate having a lowwet heat resistance (for example, TAC), it may be that the substrate isexpanded or shrunk owing to the influence of moisture. Consequently,this method was hardly said to be a method sufficient for the substratesusceptible to moisture. There was also a problem that interferencefringes are formed through multiple reflections between the layers owingto the existence of the alignment layer.

In order to remedy the viewing angle dependency of the liquid crystaldisplay adopting the VA system with use of the alignment film, a methodemploying two retardation films: a retardation film having a function asa negative C-plate and another having a function as an A plate or Bplate is generally used. As the method using such two retardation films,for example, there were used an approach as shown in FIG. 8A in which aliquid crystal cell 104 is sandwiched between a retardation film 61having a function as the negative C-plate and a retardation film 62having a function as the A plate, and an approach as shown in FIG. 8B inwhich a retardation film 61 having a function as the negative C-plateand a retardation film 62 having a function as the A plate are laminatedupon an incident side polarizing plate 102A.

The approaches, in which the problem of the viewing angle dependency isremedied by using such two retardation films, is useful in that theproblem of the viewing angle dependency can be remedied in liquidcrystal display using liquid crystal cells having various opticalcharacteristics, by changing the combination of the retardation films.However, there was a problem in that use of two retardation filmsthickened the liquid crystal displays or made a producing methodcomplicated.

Meanwhile, as mentioned above, the configuration shown in FIG. 7 isgeneral as the above retardation films. However, the retardation filmhaving such a configuration is useful in that the liquid crystalmolecules are likely to be aligned easily owing to the use of thealignment layer, but there was a problem in the adhesion propertybetween the alignment layer and the retardation layer.

To cope with such a problem, the present inventors developed, as aretardation film capable of exhibiting desired optical characteristicswithout using an alignment film, a retardation film comprising: asubstrate, and an optical functional layer which is directly formed onthe substrate and has a rodlike compound aligned randomly andhomogeneously. Such a retardation film having no alignment film isuseful in that the film has excellent adhesion property between theoptical functional layer and the substrate and that the opticalfunctional layer having the rodlike compound aligned in therandom-homogenous manner mentioned above excellently exhibits theoptical characteristics as the negative C-plate. Accordingly, such aretardation film have attracted attention as having the qualityexceeding those of the conventional retardation films in terms of thedurability and stability in the optical characteristics.

However, the above-mentioned retardation film having no alignment filmis formed by coating a composition for forming an optical functionallayer containing the above rodlike compound onto the substrate havingthe property as the negative C-plate. In some cases, it is difficult toform the random-homogenous alignment having a uniform quality with thecomposition for forming an optical functional layer conventionally used.There was also a problem that the optical functional layer becameclouded.

-   -   Patent Document 1: Japanese Patent Laid-Open (JP-A) No.        H03-67219    -   Patent Document 2: JP-A No. H04-322223    -   Patent Document 3: JP-A No. H10-312166    -   Patent Document 4: JP-A No. 2003-207644

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention, which has been made in view of theabove-mentioned problems, has a main object to provide an opticalfunctional film excellent in display quality that can exhibit excellentoptical characteristics without using an alignment film and is excellentin adhesion property between layers.

In addition, another main object of the present invention is to providea retardation film which has: a property as an optically negativeC-plate or a property as an optical A plate or B plate, and the propertyas the negative-C plate without using an alignment layer.

Moreover, yet another main object of the present invention is to providea composition for forming an optical functional layer capable of formingan optical functional layer having excellent transparency.

Means to Solve the Problems

To solve the problems, the present invention provides an opticalfunctional film comprising: a substrate having a property as anoptically negative C-plate, and an optical functional layer formed onthe substrate and having a rodlike compound, characterized in that theoptical functional layer is formed directly on the substrate, and therodlike compound forms a random homogeneous alignment in the opticalfunctional layer.

According to the present invention, since the above optical functionallayer is formed directly on the above substrate having the property asthe optically negative C-plate, the adhesion force between the substrateand the optical functional layer can be made firm. Therefore, theoptical functional film having more excellent adhesion property can beobtained, as compared with the conventional optical functional filmhaving the alignment layer.

Further, according to the present invention, since the rodlike compoundforms the random homogeneous alignment in the optical functional layer,the optical functional layer excellently exhibits the refractive indexanisotropic property and its transparency can be made high.

In the present invention, the retardation in a thickness direction (Rth)of the above substrate is preferably in a range of 20 nm to 100 nm. Thisis because, when the retardation in the thickness direction (Rth) of theabove substrate is in the above range, it becomes easy to form therandom homogeneous alignment in the above optical functional layerirrespective of the kind of the above rodlike compound. Further, whenthe Rth of the substrate is in the above range, the random homogeneousalignment having a more uniform quality can be formed.

In the above invention, the above substrate is preferably made oftriacetyl cellulose. This is because, when the substrate is made of thetriacetyl cellulose, the rodlike compound forming the above opticalfunctional layer is readily penetrated into the substrate since thetriacetyl cellulose has a molecular structure with relatively bulky sidechains. Accordingly, the adhesion property between the substrate and theoptical functional layer can be improved. Furthermore, since thetriacetyl cellulose is likely to exhibit the property as the opticallynegative C-plate, the random homogeneous alignment of the rodlikecompound is readily formed.

In the present invention, the above rodlike compound preferably has apolymerizable functional group. This is because, when the rodlikecompound has the polymerizable functional group, the rodlike compoundcan be fixed through polymerization. Therefore, the optical functionalfilm which has excellent alignment stability and is unlikely to changethe optical characteristics can be obtained by fixing the rodlikecompound in such a state that it forms the random homogeneous alignment.

Moreover, in the present invention, the above rodlike compound ispreferably a liquid crystalline material. This is because, when therodlike compound is the liquid crystalline material, the above opticalfunctional layer can exhibit excellent optical characteristics per unitthickness.

In the present invention, the above liquid crystalline material ispreferably a material exhibiting a nematic phase. This is because, whenthe liquid crystalline material is the material exhibiting the nematicphase, the random homogeneous alignment can be more effectively formed.

In the present invention, the thickness of the above optical functionallayer is preferably in a range of 0.5 μm to 10 μm. If the thickness ofthe optical functional layer is larger than the above range, it isdifficult in some cases to form the random homogeneous alignmentdepending upon the kind of the above rodlike compound. If the thicknessof the optical functional layer is smaller than the above range,necessary optical characteristics may not be exhibited in the opticalfunctional layer.

The present invention is to provide a retardation film having theretardation in the thickness direction (Rth) of the above opticalfunctional film in a range of 50 nm to 400 nm by using the above opticalfunctional film. According to the present invention, when the aboveoptical functional film is used and the retardation in the thicknessdirection (Rth) is in the above range, the retardation film suitable forimproving the viewing angle characteristics of the liquid crystaldisplay element of the VA (Vertical Alignment) system can be obtained,for example.

In the present invention, the in-plane retardation (Re) is preferably ina range of 0 nm to 5 nm. This is because, when the in-plane retardation(Re) is in the above range, the retardation film of the presentinvention can be used as a retardation film which is suitable forimproving the viewing angle characteristics of the liquid crystaldisplay element of the VA (Vertical. Alignment) system, for example.

Furthermore, in order to solve the above problems, the present inventionis to provide a retardation film comprising a substrate having aproperty of a A plate or a B plate and that of a negative C-plate, and aretardation layer containing a rodlike compound, wherein the retardationlayer is formed directly on the substrate, and the rodlike compoundforms a random homogeneous alignment in the retardation layer.

According to the present invention, since the retardation layer isformed directly on the substrate having the property of the A plate orthe B plate and that of the negative-C plate, adhesion force between thesubstrate and the retardation layer can be made firm, so that theretardation film having a more excellent adhesion property can beobtained as compared with the conventional retardation layer having thealignment layer.

Further, according to the present invention, since the rodlike compoundforms the random homogeneous alignment in the above retardation layer,the retardation layer can be made to excellently exhibit the opticalcharacteristics to function as the negative C-plate. When such aretardation layer is laminated directly on the substrate having theproperty as the A plate or the B plate and that as the negative C-plate,the retardation film as a whole can exhibit the optical characteristicsto function as the A plate or the B plate and the opticalcharacteristics to function as the C plate. Therefore, according to thepresent invention, the retardation film which contributes to thinning ofthe liquid crystal display can be obtained.

In the present invention, the in-plane retardation (Re) of the abovesubstrate is preferably in a range of 30 nm to 200 nm. This is because,when the in-plane retardation (Re) of the substrate used in the presentinvention is in the above range, the retardation film of the presentinvention can be made to have an excellent property as the A plate.

In the present invention, the retardation in the thickness direction(Rth) of the above substrate is preferably in a range of 10 nm to 150nm. This is because, when the Rth of the substrate used in the presentinvention is in the above range, the rodlike compound contained in theabove retardation layer can form the random homogeneous alignment havinga more uniform quality.

In the present invention, the above substrate is preferably made of acycloolefin polymer (COP). This is because, since the cycloolefinpolymer has low absorbability and permeability of moisture, the temporalstability in the optical characteristics of the retardation filmaccording to the present invention can be made excellent when thesubstrate used in the present invention is made of the cycloolefinpolymer (COP).

In the present invention, the above rodlike compound preferably has apolymerizable functional group. This is because, when the above rodlikecompound has the polymerizable functional group, the rodlike compoundcan be fixed through polymerization. Therefore, the retardation filmwhich has excellent alignment stability and is unlikely to change theoptical characteristics can be obtained by fixing the rodlike compoundin such a state that it forms the random homogeneous alignment.

Moreover, in the present invention, the above rodlike compound ispreferably a liquid crystalline material. This is because, when therodlike compound is the liquid crystalline material, the aboveretardation layer can exhibit excellent optical characteristics per unitthickness.

In the present invention, the above liquid crystalline material ispreferably a material exhibiting a nematic phase. This is because, whenthe liquid crystalline material is the material exhibiting the nematicphase, the random homogeneous alignment can be more effectively formed.

In the present invention, the thickness of the above retardation layeris preferably in a range of 0.3 μm to 10 μm. If the thickness of theretardation layer is larger than the above range, it is difficult insome cases to form the random homogeneous alignment depending upon thekind of the above rodlike compound. If the thickness of the retardationlayer is smaller than the above range, necessary optical characteristicsmay not be exhibited in the retardation layer.

The in-plane retardation (Re) of the retardation film of the presentinvention is preferably in a range of 30 nm to 200 nm. This is because,when the in-plane retardation (Re) is in the above range, it is possibleto obtain the retardation film suitable for improving the viewing anglecharacteristics of the liquid crystal display of the VA (VerticalAlignment) system, for example.

The retardation film of the present invention preferably has theretardation in the thickness direction (Rth) in a range of 50 nm to 300nm. This is because, when the retardation in the thickness direction(Rth) is in the above range, it is possible to obtain the retardationfilm suitable for improving the viewing angle characteristics of theliquid crystal display of the VA (Vertical Alignment) system, forexample.

Further, in order to solve the above-mentioned problems, the presentinvention is to provide a composition for forming an optical functionallayer comprising: a rodlike compound, and a mixed solvent composed of analcoholic solvent and another organic solvent, wherein the content ofthe alcoholic solvent in the mixed solvent is in a range of 5 mass % to20 mass %.

According to the present invention, when the alcoholic solvent iscontained in the above mixed solvent in the above range, the opticalfunctional layer having excellent transparency free from clouding can beformed in case that the optical functional layer is formed by using thecomposition for forming an optical functional layer of the presentinvention.

In the present invention, the above composition for forming an opticalfunctional layer is preferably used to form the optical functional layerin which the above rodlike compound forms the random homogeneousalignment. Since the optical functional layer in which the rodlikecompound forms the random homogeneous alignment can exhibit the opticalcharacteristics as the negative C-plate even if no alignment filmexists, the optical functional layer can be formed on the substrate bycoating the composition for forming an optical functional layer of thepresent invention directly thereon, for example. Thereby, the opticalfunctional layer having an excellent adhesion property to the substratecan be formed.

According to the present invention, the above rodlike compoundpreferably has a polymerizable functional group. This is because, whenthe rodlike compound has the polymerizable functional group, the rodlikecompound can be fixed through polymerization, so that the opticalfunctional layer having excellent alignment stability and excellentoptical characteristics can be formed by using the composition forforming an optical functional layer of the present invention.

Furthermore, in the present invention, the above rodlike compound ispreferably a liquid crystalline material. This is because, when therodlike compound is the liquid crystalline material, the opticalfunctional layer which excellently exhibits the optical characteristicsper unit thickness can be formed by using the composition for forming anoptical functional layer.

Further, in the present invention, the above liquid crystalline materialis preferably a material exhibiting the nematic phase. This is because,when the liquid crystalline material is the material exhibiting thenematic phase, the optical functional layer, in which the rodlikecompound forms the random homogeneous alignment having a more uniformquality, can be formed by using the composition for forming an opticalfunctional layer of the present invention.

The present invention further provides a producing method of an opticalfunctional film, comprising: a substrate having a property as a negativeC-plate, and the composition for forming an optical functional layer,characterized in that the composition for forming an optical functionallayer is coated onto the substrate to produce an optical functional filmcomprising the substrate, and the optical functional layer formeddirectly on the substrate and containing the rodlike compound formingthe random homogeneous alignment.

According to the present invention, when the optical functional layer isformed by using the above composition for forming an optical functionallayer, the optical functional film having the optical functional layerwith excellent transparency can be produced.

Further, when the optical functional layer is formed directly on thesubstrate, the optical functional film having an excellent adhesionproperty between the optical functional layer and the substrate can beproduced.

In addition, since the above rodlike compound forms the randomhomogeneous alignment in the optical functional layer of the opticalfunctional film produced by the present invention, the opticalfunctional film produced by the present invention can be made toexcellently exhibit the optical characteristics, especially the opticalcharacteristics to function as the negative C-plate.

Effects of the Invention

The present invention exhibits effects that the optical functional filmcan be obtained, which exhibits the excellent optical characteristicswithout using the alignment film and has the excellent adhesion propertybetween the optical functional layer and the substrate.

Moreover, the present invention exhibits effects that the retardationfilm can be obtained without using the alignment film, which exhibits,in a single film, the optical characteristics to function as theoptically negative C-plate or to function as the optical A plate or Bplate and the negative C-plate, and which has the excellent adhesionproperty between the retardation layer and the substrate.

Further, the composition for forming an optical functional layer of thepresent invention exhibits an effect that the optical functional layerhaving excellent transparency can be formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematically perspective view showing one embodiment of theoptical functional film of the present invention.

FIGS. 2A to 2C are each a schematically sectional view showing anotherembodiment of the optical functional film of the present invention.

FIG. 3 is a schematically sectional view showing a further anotherembodiment of the optical functional film of the present invention.

FIGS. 4A to 4C are each a schematically sectional view showing oneexample of a use embodiment of the optical functional film of thepresent invention.

FIGS. 5A to 5C are each a schematically sectional view showing anotherexample of a use embodiment of the optical functional film of thepresent invention.

FIG. 6 is a schematically sectional view showing one example of ageneral liquid crystal display.

FIG. 7 is a schematically sectional view showing one example of theconventional retardation film.

FIGS. 8A and 8B are each a schematically sectional view showing oneexample of the liquid crystal display using two retardation films.

EXPLANATION OF REFERENCES

1 substrate 2 optical functional layer 3 rodlike compound 10 opticalfunctional film 21 substrate 22 retardation layer 23 rodlike compound 20retardation film 30, 40 polarizing plate 51 film for protecting apolarizing plate 52 polarizer 60, 61, 62 retardation film 71 substrate72 alignment layer 73 retardation layer 100 liquid crystal display 102A,102B polarizing plate 104 liquid crystal cell

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, the optical functional film, the retardation film, thecomposition for forming an optical functional layer and the producingmethod of an optical functional film according to the present inventionwill be explained in detail.

A. Optical Functional Film

First, the optical functional film of the present invention will beexplained. The optical functional film of the present inventioncomprises: a substrate having a property as an optically negativeC-plate, and an optical functional layer formed directly on thesubstrate and having a rod-like compound, wherein the optical functionallayer is formed directly on the substrate, and the rodlike compoundforms a random homogeneous alignment in the optical functional layer.

Next, the optical functional film according to the present inventionwill be explained with reference to the drawings. FIG. 1 is aschematically perspective view of one embodiment of the opticalfunctional film of the present invention. As shown in FIG. 1, theoptical functional film 10 of the present invention comprises asubstrate 1 and an optical functional layer 2 formed directly on thesubstrate 1. In the optical functional film 10 of the present invention,the substrate 1 has the property as the optically negative C-plate, andthe optical functional layer 2 contains the rod-like compound 3 whichforms a random homogeneous alignment. As shown in FIG. 1, the opticalfunctional film 10 of the present invention has the configuration thatthe optical functional layer 2 is formed directly on the substrate 1 andthat the film does not have the alignment layer as the indispensableconstituent element unlike the conventional optical film as shown inFIG. 7.

Since the optical functional layer is formed directly on the substratein the optical functional film according to the present invention asillustrated in FIG. 1, the substrate can be firmly adhered to theoptical functional layer, so that the film has a merit that nodelamination or the like will occur with lapse of time. Further, withimprovement in the adhesion property, the optical functional film hasmerits, for example, that the alkaline resistance and reworkability areimproved.

It is considered that the formation of the optical functional layerdirectly on the substrate like this improves the adhesion force betweenthem through the following mechanism. That is, since the formation ofthe optical functional layer directly on the substrate enables therod-like molecules contained in the optical functional layer to bepenetrated into the substrate from the surface thereof, there is noclear interface at a bonding portion between the substrate and theoptical functional layer, and the bonding portion is in a “mixed” stateof them. Thus, it is considered that the adhesion property isconspicuously improved owing to this as compared with the bondingthrough the conventional interface interaction.

In addition, the conventional optical functional film with the alignmentlayer has the problem that light undergoes multiple reflections in theinterface between the alignment layer and the optical functional layerand the interface between the alignment layer and the substrate to causeinterference fringes. However, according to the optical functional filmof the present invention, there is no clear interface, because the filmhas no alignment layer as mentioned above and the bonding portionbetween the substrate and the optical functional layer is in the “mixed”state. Therefore, the film has the merits that the above multiplereflections do not occur and therefore, the deterioration in qualitydoes not occur owing to the interference fringes.

Next, the random homogeneous alignment in the present invention will beexplained. The random homogeneous alignment in the present invention isan alignment state which is formed by the rodlike compound contained inthe above optical functional layer. Since the rodlike compound has suchan alignment state, the optical characteristics of the opticalfunctional film of the present invention can be made excellent.

The random homogeneous alignment of the rodlike compound in the presentinvention has at least three features as mentioned below. That is, therandom homogeneous alignment in the present invention has at leastfollowing three features:

first, when the optical functional layer is viewed just from thevertical direction to the surface of the optical functional layer, thealignment directions of the rodlike compounds are random (hereinafter,it may be referred to simply as “irregularity”);

second, sizes of domains formed by the rodlike compounds in the opticalfunctional layer are smaller than the wavelengths in the visible lightzone (hereinafter, it may be referred to simply as “dispersibility”);and

third, the rodlike compounds are aligned in-plane in the opticalfunctional layer (hereinafter, it may be referred to simply as “in-planealignment properties”).

Next, such a random homogeneous alignment in the present invention willbe explained with reference to the drawings. FIG. 2A is a schematic viewin which the optical functional film according to the present inventionis viewed just from that vertical direction to the surface of theoptical functional layer which is shown by A in FIG. 1 mentioned above.Meanwhile, FIGS. 2B and 2C are each a sectional view from B-B′ lineararrows in FIG. 2A.

First, “irregularity” possessed by the random homogeneous alignment inthe present invention will be explained with reference to FIG. 2A. The“irregularity” means that when the optical functional film 10 of thepresent invention is viewed just from the vertical direction to thesurface of the optical functional layer 2 as shown in FIG. 2A, therodlike compounds 3 is aligned randomly in the optical functional layer2.

Here, when the alignment directions of the rodlike compound 3 are to beexplained in the present invention, the long-axis direction of themolecule (hereinafter, referred to as “molecular axis) shown by “a” inFIG. 2A is considered as a reference. Therefore, that the alignmentdirections of the rodlike compounds are random means that the molecularaxes “a” of the rodlike compound 3 contained in the optical functionallayer are directed randomly.

When the rodlike compound has a cholesterolic structure other than thesequence state illustrated in FIG. 2A, this formally corresponds to the“irregularity”, because the directions of the molecular axes “a” arerandom as a whole. However, the state resulting from the cholesterolicstructure is not included in the “irregularity” in the presentinvention.

Next, the “dispersibility” possessed by the random homogeneous alignmentin the present invention will explained with reference to FIG. 2A. The“dispersibility” means that when a domain “b” is formed by the rodlikecompound 3 in the optical functional layer 2 as shown in FIG. 2A, thesize of the domain “b” is smaller than the wavelengths in the visiblelight zone. In the present invention, the smaller the size of the domain“b”, the more preferable it is. It is the most preferable that therodlike compounds are dispersed in a single molecular state.

The “in-plane alignment properties” possessed by the random homogeneousalignment in the present invention will be explained with reference toFIG. 2B. The “in-plane alignment properties” means that as shown in FIG.2B, the rodlike compounds 3 aligns the molecular axes “a”, in theoptical functional layer 2, substantially vertical to the normaldirection A of the optical functional layer 2. The “in-plane alignmentproperties” in the present invention not only means the case where asshown in FIG. 2B, the molecular axes “a” of all the rodlike compound 3in the optical functional layer 2 are substantially vertical to thenormal direction A, but also it includes a case where even if there arerodlike compound 3 of which molecular axes “a′” are not vertical, in theoptical functional layer 2, to the normal direction A as shown in FIG.2C, the average direction of the molecular axes “a” of the rodlikecompound 3 existing in the optical functional layer 2 are substantiallyvertical to the normal direction A.

According to the optical functional film of the present invention, sincethe above rodlike compound forms the random homogeneous alignment, therelation: nx=ny>nz is realized among a refractive index “nx” in anx-direction, a refractive index “ny” in a y-direction and a refractiveindex “nz” in a z-direction shown in FIG. 1. The optical functional filmof the present invention can be favorably used as the retardation filmhaving the property as the negative C-plate.

As explained above, the random homogeneous alignment in the presentinvention is featured by exhibiting at least “irregularity”,“dispersibility” and “in-plane alignment properties”. That the opticalfunctional film of the present invention possesses these features can beconfirmed by the following methods.

First, a method for confirming the “irregularity” possessed by therandom homogeneous alignment in the present invention will be explained.The “irregularity” can be confirmed by evaluating the in-planeretardation (Re) of the optical functional layer constituting theoptical functional film of the present invention and by evaluatingwhether a selective reflection wavelength resulting from thecholesterolic structure exists or not.

That is, that the rodlike compound is aligned randomly can be confirmedby evaluating the Re of the optical functional layer constituting theoptical functional film of the present invention, and that the rodlikecompounds do not form the cholesterolic structure can be confirmed bybased on whether the selective reflection wavelength exists or not.

That the above rodlike compounds are aligned randomly can be confirmedby ascertaining that the value of the in-plane retardation (Re) of theoptical functional layer in the range showing that the rodlike compoundis in the random alignment. Particularly, in the present invention, thein-plane retardation (Re) of the optical functional layer is preferablyin a range of 0 nm to 5 nm. Here, the Re is a value expressed by aformula: Re=(Nx−Ny)×d in which Nx and Ny are respectively a refractiveindex in the leading phase axis direction (the direction with thesmallest refractive index) and a refractive index in the lagging phaseaxis direction (the direction with the largest refractive index) in theplane of the optical functional layer constituting the opticalfunctional film of the present invention, and “d” is the thickness (nm)of the optical functional layer in the plane of the retardation layerconstituting the optical functional film of the present invention.

Here, that the above rodlike compound is in the random alignment can beconfirmed by the Re for the following reason. That is, as is clear fromthe above definition formula, Re is a parameter showing a differencebetween the refractive indexes in the in-plane directions. When therodlike compounds are aligned regularly in one direction in the opticalfunctional layer, the above refractory index difference tends toincrease, because the refractive index becomes greater in a specificdirection. On the other hand, when the rodlike compound is in the randomalignment, the above refractive index difference tends to decrease,because the refractive index in a specific direction inside the plane ofthe optical functional layer does not increase. Therefore, the“irregularity” can be evaluated by estimating the Re which denotes sucha refractive index difference.

For example, the Re of the above optical functional layer can bedetermined by subtracting the Re indicated by other layer(s) than theoptical functional layer from the Re of the optical functional film.That is, the Re of the optical functional layer can be determined bymeasuring the Re of the entire optical functional film and the Re of aremainder in which the optical functional layer is removed from theoptical functional film, and subtracting the latter Re from the formerRe. For example, Re can be measured by a parallel Nicol rotation methodwith use of KOBRA-WR manufactured by Oji Scientific Instruments.

That the above rodlike compound has no cholesterolic structure can beevaluated by confirming that the optical functional layer in the presentinvention has no selective reflection wavelength, with use of aUV-VIS-NIR spectrophotometer (UV-3100 or the like) manufactured byShimadzu Corporation. For, when the rodlike compound takes thecholesterolic structure, it is characterized in that it has theselective reflection wavelength depending upon the spiral pitch of thecholesterolic structure.

Next, a method for confirming the “dispersibility” possessed by therandom homogeneous alignment in the present invention will be explained.The “dispersibility” can be confirmed by ascertaining that the hazevalue of the optical functional layer constituting the opticalfunctional film of the present invention is in a range denoting that thesizes of the domains of the above rodlike compounds are not more thanthe wavelengths in the visible light zone. Particularly, in the presentinvention, the haze value of the optical functional layer is preferablyin a range of 0% to 5%.

Here, the haze value of the optical functional layer can be determinedby subtracting the haze value of the other layer(s) than the opticalfunctional layer from that of the optical functional film, for example.That is, the haze value of the optical functional layer can bedetermined by measuring the haze value of the entire optical functionalfilm and that of a remainder in which the optical functional layer isremoved from the optical functional film, and subtracting the latterhaze value from the former haze value. A value measured according to JISK7105 is used as the above haze value.

Here, that the “dispersibility” is possessed or that the sizes of thedomains formed by the rodlike compounds are smaller than the wavelengthsin the visible light zone is to be confirmed by the haze for thefollowing reason. That is, if the rodlike compound forms a domain andthe size of the domain is greater than the wavelength of the visiblelight, the optical functional layer tends to be clouded, because thevisible light is scattered in the above optical functional layer.Therefore, the “dispersibility” can be evaluated by measuring the hazeof the optical functional layer in the visible light zone.

The concrete size of the above domain in the present invention ispreferably not more than the wavelengths of the visible lights, that is,not more than 380 nm, more preferably not more than 350 nm, andparticularly preferably not more than 200 nm. In the present invention,note that since the rodlike compound is dispersed in the form of singlemolecules, the lower limit of the above domains is that of the singlemolecule of the rodlike compound. The size of such a domain can beevaluated by observing the optical functional layer with a polarizationmicroscope, an AFM, an SEM or a TEM.

Next, a method for confirming the “in-plane alignment properties”possessed by the random homogeneous alignment in the present inventionwill be explained. The “in-plane alignment properties” can be confirmedby ascertaining that the Re value of the optical functional layerconstituting the optical functional film of the present invention is inthe above-mentioned range and that the optical functional layer in thepresent invention has the retardation value in the thickness direction(Rth), which denotes the property as the optically negative C-plate.Particularly, the retardation in the thickness direction (Rth) of theoptical functional layer in the present invention is preferably in arange of 50 nm to 400 nm. Here, the Rth value is a retardation value inthe thickness direction, which is represented by a formula:Rth={(Nx+Ny)/2−Nz}×d in which Nx and Ny are respectively a refractiveindex in the leading phase axis direction (the direction with thesmallest refractive index) and a refractive index in the lagging phaseaxis direction (the direction with the largest refractive index) in theplane of the optical functional layer constituting the opticalfunctional film of the present invention, Nz is a refractive index inthe thickness direction, and “d” is the thickness (nm) of the opticalfunctional layer. Here, the Rth in the present invention denotes anabsolute value of that represented by the above formula.

Here, that the rodlike compound possesses the “in-plane alignmentproperties” can be confirmed by the Re and the Rth for the followingreason. That is, as is clear from the above definition formula, Rth is aparameter resulting from a difference between the average value of therefractive indexes in the in-plane directions and the refractive indexin the thickness direction. As mentioned above, since the Re value ofthe optical functional layer gives a value in a certain range from the“irregularity”, the Rth value depends upon the refractive index (Nz) inthe thickness direction. Here, since the refractive index in thethickness direction (Nz) tends to decrease because of the in-planealignment of the rodlike compound, the Rth value tends to increase inthis case. Therefore, the “in-plane alignment properties” can beevaluated when the Rth value of the optical functional layer is in theabove range.

The Rth of the above optical functional layer can be determined bysubtracting the Rth denoted by the other layer(s) than the opticalfunctional layer from the Rth of the optical functional film, forexample. That is, the Rth of the optical functional layer can bedetermined by measuring the Rth of the entire optical functional filmand the Rth of a remainder in which the optical functional layer isremoved from the optical functional film, and subtracting the latter Rthfrom the former Rth. The Rth can be measured by the parallel Nicolrotation method with use of the KOBRA-WR manufactured by Oji ScientificInstruments.

As mentioned above, the optical functional film according to the presentinvention comprises the substrate and the optical functional layerformed directly on the substrate. In the following, the configuration ofsuch an optical functional film of the present invention will beexplained in detail.

1. Optical Functional Layer

First, the optical functional layer constituting the optical functionalfilm of the present invention will be explained. The optical functionallayer in the present invention is formed directly on the below-mentionedsubstrate. When the optical functional layer in the present invention isdirectly formed on the substrate like this, it can be firmly adhered tothe substrate. In addition, the optical functional layer in the presentinvention contains the rodlike compound, and the rodlike compound formsthe random homogeneous alignment. Since such a rodlike compound formsthe random homogeneous alignment, excellent optical characteristics canbe exhibited in the optical functional film of the present inventionwithout the alignment layer. In the following, such an opticalfunctional layer will be explained in detail.

(1) Rodlike Compound

The rodlike compound used in the present invention will be explained.The rodlike compound used in the present invention is not particularlylimited, so long as it can form the random homogeneous alignment in theoptical functional layer.

Here, the “rodlike compound” in the present invention means a compoundin which a main skeleton of the molecular structure is rod-like. As thecompound having such rod-like main skeletons, mention may be made ofazomethin compounds, azoxy compounds, cyanobiphenyl compounds,cyanophenyl esters, benzoic acid esters, cyclohexane carboxylic acidphenyl esters, cyanophenyl cyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenyl pyrimidines, phenyl dioxanes,tolans, and alkenylcyclohexyl benzonitriles. Further, not only the abovelow-molecular liquid crystalline compounds but also high-molecularliquid crystalline compounds can be used.

As the rodlike compound used in the present invention, a compound havinga relatively small molecular weight is favorably used. Morespecifically, a compound having a molecular weight in a range of 200 to1200, particularly in a range of 400 to 800 is favorably used. This isbecause, when the molecular weight is in the above range, the rodlikecompound is likely to be penetrated into the substrate mentioned later.Consequently, a “mixed” state is likely to be formed at the bondingposition between the substrate and the optical functional layer, and theadhesion property between the substrate and the optical functional layercan be improved.

As to the above-mentioned molecular weight concerning the rodlikecompound being a material having a polymerizable functional group to bedescribed later, it refers to the molecular weight before thepolymerization.

Moreover, it is preferable that the rodlike compound used in the presentinvention is a liquid crystalline material showing the liquidcrystalline property. Since the rodlike compound is a liquid crystallinematerial, the above optical functional layer can be provided with theexcellent optical characteristic realizing property per unit thickness.Moreover, it is preferable that the rodlike compound used in the presentinvention is a liquid crystalline material showing the nematic phaseamong the liquid crystalline materials. A liquid crystalline materialshowing the nematic phase can form a random homogeneous alignmentrelatively easily.

Furthermore, it is preferable that the above liquid crystalline materialshowing the nematic phase is a molecule having a spacer on both ends ofthe mesogen. Since a liquid crystalline material having a spacer on bothends of the mesogen has the excellent flexibility, clouding of theoptical functional layer in the present invention can effectively beprevented.

As the rodlike compound used in the present invention, those having apolymerizable functional group in a molecule can be used preferably. Inparticular, those having a three-dimensionally cross-linkablepolymerizable functional group are preferable. Since the rodlikecompound has a polymerizable functional group, the rodlike compound canbe fixed by the polymerization. By fixing the rodlike compound in astate where the random homogenous alignment is formed, an opticalfunctional film having the sequence stability and having difficulty incausing changes in optical characteristics can be obtained. In thepresent invention, the above-mentioned rodlike compound having apolymerizable functional group and the above-mentioned rodlike compoundnot having a polymerizable functional group can be used as a mixture.

The “three-dimensional cross-linking” mentioned above denotes tothree-dimensionally polymerize the liquid crystalline molecules witheach other so as to be in a mesh-like (network) structure state.

As the polymerizable functional group, various polymerizable functionalgroups to be polymerized by the function of the ionizing radiation suchas the ultraviolet ray and the electron beam, or the heat can be usedwithout particular limitation. As the representative examples of thesepolymerizable functional groups, a radically polymerizable functionalgroup, or a cation polymerizable functional group can be presented.Furthermore, as the representative examples of the radicallypolymerizable functional group, a functional group having at least oneaddition polymerizable ethylenically unsaturated double bond can bepresented. As the specific examples, a vinyl group having or not havinga substituent, or an acrylate group (the general term including anacryloyl group, a methacryloyl group, an acryloyloxy group, and amethacryloyloxy group) can be presented. Moreover, as the specificexamples of the cation polymerizable functional group, an epoxy group,or the like can be presented. Additionally, as the polymerizablefunctional group, for example, an isocyanate group or an unsaturatedtriple bond can be presented. Among these examples, in terms of theprocess, a functional group having an ethylenically unsaturated doublebond can be used preferably.

As the rodlike compound in the present invention, a liquid crystallinematerial showing the liquid crystalline property, having theabove-mentioned polymerizable functional group on the end isparticularly preferable. For example, by using a nematic liquidcrystalline material having a polymerizable functional group on the bothends, a mesh-like (network) structure state can be provided by thethree-dimensional polymerization with each other so as to obtain anoptical functional layer having the sequence stability and excellentoptical characteristic realizing properties. Moreover, even in the caseof one having a polymerizable functional group on one end, it can havethe sequence stability by cross-linking with the other molecules. Assuch a rodlike compound, the compounds represented by the followingformulae (1) to (6) can be presented.

Here, the liquid crystalline materials represented by the chemicalformulae (1), (2), (5) and (6) can be prepared according to the methodsdisclosed by D. J. Broer et, al., Makromol. Chem. 190, 3201-3215 (1989),or by D. J. Broer et, al., Makromol. Chem. 190, 2250 (1989), or by asimilar method. Moreover, preparation of the liquid crystallinematerials represented by the chemical formulae (3) and (4) is disclosedin DE 195,04,224.

Moreover, as the specific examples of the nematic liquid crystallinematerial having an acrylate group on the end, those represented by thefollowing chemical formulae (7) to (17) can also be presented.

In the present invention, as the rodlike compound, only one kind may beused, or two or more kinds may be used as a mixture.

For example, when a mixture of a liquid crystalline material having oneor more polymerizable functional groups on the both ends and a liquidcrystalline material having one or more polymerizable functional groupson one end is used, it is preferable because the polymerization density(cross-linking density) and the optical characteristics can be adjustedoptionally by adjustment of the composition ratio thereof.

(2) Other Compounds

In the optical functional layer in the present invention, othercompound(s) may be included besides the above-mentioned rodlikecompound. Such other compound is not particularly limited, so long as itdoes not disturb the random homogeneous alignment of the rodlikecompound. As such other compound, a polymerizable material ordinarilyused in a hard coat agent can be given, for example.

As the above polymerizable material, mention may be made, for example,of a polyester (metha)acrylate obtained by reacting (metha)acrylic acidwith a polyester prepolymer which is obtained by condensing a polyvalentalcohol with a monobasic acid or a polybasic acid; apolyurethane(metha)acrylate obtained by mutually reacting a compoundhaving a polyol group and a compound having two isocyanate groups andthen reacting the reaction product thereof with (metha)acrylic acid;photopolymerizable compounds, such as epoxy(metha)acrylates, obtained byreacting (metha)acrylic acid with an epoxy resin such as a bisphenol Atype epoxy resin, a bisphenol F type epoxy resin, a novolac type epoxyresin, a polycarboxylic acid polyglycidyl ester, polyol polyglycidylether, an aliphatic or alicyclic epoxy, an amino group epoxy resin, atriphenol methane type epoxy resin or a dihydroxy benzene type epoxyresin; a photopolymerizable liquid crystalline compound having anacrylic group or a methacrylic group, etc.

(3) Optical Functional Layer

The thickness of the optical functional layer in the present inventionis not particularly limited, so long as it is in a range in whichdesired optical characteristics can be imparted upon the opticalfunctional layer, depending upon the kind of the above rodlike compound.Particularly, in the present invention, the thickness of the opticalfunctional layer is preferably in a range of 0.5 μm to 10 μm, morepreferably in a range of 0.5 μm to 5 μm, and particularly preferably ina range of 1 μm to 3 μm. If the thickness of the optical functionallayer is greater than the above range, it may be that the “in-planealignment properties” as one of the features of the random homogeneousalignment is damaged, so that the desired optical characteristics arenot obtained. If the thickness is smaller than the above range, it mayalso be that the targeted optical characteristics are not obtaineddepending upon the kind of the above rodlike compound.

Here, in the optical functional film of the present invention, when thebonding portion between the optical functional layer and the substratementioned later possess the mixed region in which both of them are“mixed”, the thickness of the mixed region is not included in thethickness of the above optical functional layer.

From the standpoint of the “irregularity” and the “in-plane alignmentproperties” possessed by the above random homogeneous alignment, asmentioned above, the retardation (Re) of the optical functional layer inthe present invention is preferably in the range of 0 nm to 5 nm, morepreferably in a range of 0 nm to 3 nm in that range, and particularlypreferably in a range of 0 nm to 1 nm. Here, the definition and themeasuring method of the Re value are as mentioned above, and thusexplanation is omitted here.

Furthermore, as to the optical functional layer in the presentinvention, the value (Re/d) obtained by dividing the retardation (Re(nm)) of the optical functional layer by the thickness “d” (pm) of theoptical functional layer is preferably in a range of 0 to 0.2, morepreferably in a range of 0 to 0.1, and particularly preferably in arange of 0 to 0.05.

From the standpoint of the “in-plane alignment properties” possessed bythe above random homogeneous alignment, as mentioned above, theretardation in the thickness direction (Rth) of the optical functionallayer in the present invention is preferably in the range of 50 nm to400 nm, more preferably in a range of 50 nm to 300 nm in that range, andparticularly preferably in a range of 50 nm to 200 nm. Here, thedefinition and the measuring method of the Rth value are as mentionedabove, and thus explanation is omitted here.

Meanwhile, as to the optical functional layer in the present invention,the value (Rth/d) which is obtained by dividing the retardation value inthe thickness direction (Rth(nm)) of the optical functional layer by thethickness (d(μm)) of the optical functional layer is preferably in arange of 0.5 to 13, more preferably in a range of 0.5 to 10, andparticularly preferably in a range of 0.5 to 7.

From the standpoint of the “dispersibility” possessed by the aboverandom homogeneous alignment, as mentioned above, the haze of theoptical functional layer in the present invention is preferably in arange of 0% to 5%, more preferably in a range of 0% to 1%, andparticularly preferably in a range of 0% to 0.5%. Here, the definitionand the measuring method of the haze are as mentioned above, and thusexplanation is omitted here.

The configuration of the optical functional layer in the presentinvention is not limited to a single layer structure, but the opticalfunctional layer may have a configuration in which a plurality of layersis laminated. In the case of the configuration in which the plurallayers are laminated, the layers having the same composition may belaminated, or the plural layers having different compositions may belaminated. Further, in the case of the configuration in which theoptical functional layer is composed of the plural layers, at least theoptical functional layer laminated directly on the substrate has only topossess the rodlike compound forming the random homogeneous alignment.

2. Substrate

Next, the substrate used in the present invention will be explained. Thesubstrate used in the present invention has the function as theoptically negative C-plate. Further, as mentioned later, since the aboveoptical functional layer is formed directly on the substrate in theoptical functional film of the present invention, the rodlike compoundcontained in the optical functional layer forms the random homogeneousalignment. Therefore, the substrate used in the present invention has afunction as a so-called alignment film for making the above rodlikecompound form the random homogeneous alignment. In the following, thesubstrate used in the present invention will be explained.

The substrate used in the present invention is not particularly limited,so long as it has the property as the optically negative C-plate. Here,that “has the property as the optically negative C-plate” in the presentinvention means that the relationship: Nx=Ny>Nz is satisfied in which Nxand Ny are respectively the refractive indexes in arbitrary x-directionand y-direction in the plane of the substrate sheet, and Nz is therefractive index in the thickness direction.

The substrate having the property as the optically negative C-plate isused as the substrate in the present invention for the following reason.That is, as mentioned above, the substrate in the present inventionfunctions as the so-called alignment film for making the rodlikecompound form the random homogeneous alignment. If the substrate doesnot have the property as the optically negative C-plate, the rodlikecompound cannot form the random homogeneous alignment.

In the present invention, the mechanism in which the rodlike compoundforms the random homogeneous alignment when the optical functional layercontaining the rodlike compound is formed on the substrate having theproperty as the optically negative C-plate is not clear. But, this isconsidered to be based on the following mechanism.

That is, for instance, if a case of the substrate being made of apolymer material is considered, it is thought that when the substratehas the property as the optically negative C-plate, the polymer materialconstituting the substrate is aligned random, without specificregularity, in the in-plane direction. It is thought that when the aboverodlike compound is applied onto the substrate having the polymermaterial aligned randomly in the in-plane direction on the surface, therodlike compound partially penetrates into the substrate, and themolecular axes are aligned along those molecular axes of the polymermaterial which are aligned randomly. It is thought that such a mechanismmakes the substrate having the optically negative C-plate exhibit thefunction as the alignment film to form the random homogeneous alignment.

It is considered that the above substrate has the function as thealignment film for making the rodlike compound form the randomhomogeneous alignment through the above-mentioned mechanism. Therefore,the substrate used in the present invention must have an alignmentcontrolling power for the rodlike compound, and must take aconfiguration in which that material constituting the substrate whichexhibits the property as the optically negative C-plate must be presentat the surface of the substrate. Accordingly, even if the substrate hasthe property as the optically negative C-plate, that configurationcannot be used as the substrate in the present invention, in which whenthe optical functional layer is formed on the substrate, the aboverodlike compound cannot contact that material constituting the substratewhich has the alignment controlling power for the rodlike compound.

As such a substrate being unable to be used in the present invention,for example, mention may be made of a substrate having a configurationthat a supporting body having a construction made of a polymer materialalone and having the property as the optically negative C-plate islaminated with a retardation layer containing an optically anisotropicmaterial with a refractive index anisotropic property. In the substratehaving such a configuration, the polymer material constituting thesupporting body is that material constituting the substrate which hasthe alignment controlling power to the above rodlike compound. However,when the above optical functional layer is formed on the retardationlayer, the rodlike compound cannot contact the polymer material due tothe presence of the retardation layer. Therefore, the substrate havingsuch a configuration is not included in the substrate, in the presentinvention, even having the property as the optically negative C-plate.

The property of the optically negative C-plate of the substrate used inthe present invention may be appropriately selected depending upon thekind of the rodlike compound used in the above optical functional layer,the optical characteristics required for the optical functional film ofthe present invention, etc. Especially, in the present invention, theretardation in the thickness direction (Rth) of the substrate ispreferably in a range of 20 nm to 100 nm, particularly preferably in arange of 25 nm to 80 nm, and most preferably in a range of 30 nm to 60nm in that range. This is because, when the retardation in the thicknessdirection (Rth) of the substrate is in the above range, the randomhomogeneous alignment is easily formed in the optical functional layer,irrespective of the kind of the rodlike compound. Further, when the Rthof the substrate is in the above range, the random homogeneous alignmenthaving a uniform quality can be formed.

Here, the definition and the measuring method of the Rth are identicalwith those explained in the above section “1. Optical functional layer”,and thus explanation thereof is omitted here.

In addition, from the standpoint of the formation of the randomhomogeneous alignment having the uniform quality, the Rth is in theabove range, and the in-plane retardation (Re) is preferably in a rangeof 0 nm to 300 nm, particularly preferably in a range of 0 nm to 150 nm,and more preferably in a range of 0 nm to 125 nm.

The transparency of the substrate used in the present invention may bedetermined optionally according to the transparency required to theoptical functional film of the present invention, or the like. Ingeneral, it is preferable that the transmittance in a visible light zoneis 80% or more, and it is more preferably 90% or more. This is because,if the transmittance is low, the selection ranges in the rodlikecompound and the like becomes narrow. Here, the transmittance of thesubstrate can be measured according to the JIS K7361-1 (Testing methodof the total light transmittance of a plastic-transparent material).

The thickness of the substrate used in the present invention is notparticularly limited as long as necessary self supporting properties canbe obtained according to the application of the optical functional filmof the present invention, or the like. In general, it is preferably inthe range of 10 μm to 188 μm; it is more preferably in the range of 20μm to 125 μm; and it is particularly preferably in the range of 30 μm to80 μm. In the case the thickness of the substrate is thinner than theabove-mentioned range, the necessary self supporting properties may notbe provided to the optical functional film of the present invention.Moreover, in the case the thickness is thicker than the above-mentionedrange, for example, at the time of cutting process of the opticalfunctional film of the present invention, the process waste may beincreased or wear of the cutting blade may be promoted.

Here, in the optical functional film of the present invention, in thecase the bonding portion of the optical functional layer and thesubstrate to be explained has a mixed region with themselves “mixed”,the thickness of the optical functional layer includes the thickness ofthe above-mentioned mixed region.

As the substrate used in the present invention, either a flexiblematerial having the flexible property or a rigid material without theflexible property can be used as long as it has the above-mentionedoptical properties, however, it is preferable to use a flexiblematerial. Since the flexible material is used, the production processfor the optical functional film of the present invention can be providedas a roll-to-roll process so that an optical functional film having theexcellent productivity can be obtained.

As the material for the above-mentioned flexible material, cellulosederivatives, a norbornen based polymer, a cycloolefin based polymer,polymethyl methacrylate, polyvinyl alcohol, polyimide, polyallylate,polyethylene terephthalate, polysulfone, polyether sulfone, amorphouspolyolefin, a modified acrylic based polymer, polystyrene, an epoxyresin, polycarbonate, polyesters, or the like can be presented. Amongthem, cellulose derivatives can be used preferably since cellulosederivatives have especially excellent optical isotropy and can providean optical functional film excellent in optical characteristics.

As the cellulose derivatives used in the present invention, celluloseesters can be used preferably. Furthermore, among the cellulose esters,it is preferable to use cellulose acylates. Since the cellulose acylatesare used widely in the industrial field, it is advantageous in terms ofthe accessibility convenience.

As the cellulose acylates, lower fatty acid esters having 2 to 4 carbonatoms are preferable. The lower fatty acid ester may be one including asingle lower fatty acid ester such as a cellulose acetate, or it may beone including a plurality of lower fatty acid esters such as a celluloseacetate butylate and a cellulose acetate propionate.

In the present invention, among the above-mentioned lower fatty acidesters, a cellulose acetate can be used particularly preferably. As thecellulose acetate, it is preferable to use triacetyl cellulose havingthe average acetification degree of 57.5 to 62.50 (substitution degree:2.6 to 3.0). Since triacetyl cellulose has the molecular structurehaving relatively bulky side chains, when the substrate is made of thetriacetyl cellulose, the rodlike compound forming the above opticalfunctional layer is likely to penetrate into the substrate, and thus theadhesion property between the substrate and the optical functional layercan be improved. In addition, since triacetyl cellulose readily exhibitsthe property as the optically negative C-plate, the random homogeneousalignment of the rodlike compound is easily formed. Here, anacetification degree means an amount of bonded acetic acid per unit massof cellulose. The acetification degree can be determined throughmeasurement and calculation of the acetification degree in ASTM:D-817-91 (a testing method for cellulose acetate, etc). Note that theacetification degree of triacetyl cellulose constituting the triacetylcellulose film can be determined by the above method after impuritiessuch as a plasticizer, etc. contained in the film are removed.

As the norbornen based polymer, a cycloolefin polymer (COP) and acycloolefin copolymer (COC) can be presented. In the present invention,it is preferable to use a cycloolefin polymer. Since the cycloolefinpolymer has low absorbing properties and transmitting properties of themoisture content, by using the substrate made of the cycloolefin polymerin the present invention, the optical functional film of the presentinvention can be provided with the excellent temporal stability of theoptical characteristics.

The configuration of the substrate in the present invention is notlimited to a single layer configuration, but it may have a configurationin which a plurality of layers is laminated. When the substrate has theconfiguration in which a plurality of the layers is laminated, thelayers having the same composition may be laminated, or the plurallayers having different compositions may be laminated.

As the configuration of the substrate in which the plural layers havingthe different compositions are laminated, for instance, a configurationis given by example, in which a supporting body having excellentmoisture permeability and self-supporting property is laminated upon afilm made of a material, such as triacetyl cellulose, to make the aboverodlike compound to be aligned random and homogeneously.

3. Optical Functional Film

Since one of the features of the optical functional film of the presentinvention is that the optical functional layer is formed directly on thesubstrate, the rodlike compound contained in the optical functionallayer penetrates into the above substrate, and the mixed region in whichboth are “mixed” is formed at the bonding portion between the substrateand the optical functional layer. The thickness of such a mixed regionis not particularly limited, so long as the above random homogeneousalignment can be formed, and the adhesion force between the substrateand the optical functional layer can be set in a desired range.Especially, in the present invention, the thickness of the mixed regionis preferably in a range of 0.1 μm to 10 μm, particularly preferably ina range of 0.5 μm to 5 μm, and most preferably in a range of 1 μm to 3μm in that range.

The distributed state of the rodlike compound in the mixed region is notparticularly limited, either, so long as the random homogeneousalignment can be formed, and adhesion force between the substrate andthe optical functional layer can be set in a desired range. As the abovedistributed state of the rodlike compound, a configuration in which therodlike compound exists uniformly in the thickness direction of thesubstrate and a configuration in which the rodlike compound has aconcentration gradient in the thickness direction of the substrate aregiven by way of example. Either of the configurations can be favorablyused in the present invention.

Meanwhile, the confirmation of the presence of the mixed region and theconfirmation of the distributed state of the rodlike compound in themixed region can be made by a TOE-SIMS method.

The optical functional film of the present invention may have otherconfigurations other than the substrate and the optical functionallayer. As the other configurations, for example, a reflection preventinglayer, an ultraviolet ray absorbing layer, an infrared ray absorbinglayer, or a charge preventing layer can be presented.

The reflection preventing layer used in the present invention is notparticularly limited. For example, one comprising a low refractive indexlayer formed on a transparent substrate film, in which the layer made ofa substance having a refractive index lower than that of the transparentsubstrate is formed; or one comprising a high refractive index layermade of a substance having a refractive index higher than that of thetransparent substrate and a low refractive index layer made of asubstance having a refractive index lower than that of the transparentsubstrate formed in this order alternately by each one or more layers ona transparent substrate film can be presented. These high refractiveindex layer and the low refractive index layer are formed such as byvacuum vapor deposition or coating so as to have the optical thicknessrepresented by the multiple of the geometric thickness and therefractive index by ¼ of the wavelength of the light beam to have thereflection prevention. As the constituent material for the highrefractive index layer, titanium oxide, zinc sulfide, or the like; asthe constituent material for the low refractive index layer, magnesiumfluoride, cryolite, or the like can be used.

Moreover, the ultraviolet ray absorbing layer used in the presentinvention is not particularly limited. For example, a film formed byadding an ultraviolet ray absorbing agent made of such as a benzotriazolbased compound, a benzophenone based compound, or a salicylate basedcompound in a film of such as a polyester resin or an acrylic resin canbe presented.

Moreover, the infrared ray absorbing layer used in the present inventionis not particularly limited. For example, one formed by such as coatingan infrared ray absorbing layer on a film substrate of a polyester resincan be presented. As the infrared ray absorbing layer, for example, oneformed by adding an infrared ray absorbing agent made of such as adiimmonium based compound or a phthalocyanine based compound in a binderresin made of such as an acrylic resin or a polyester resin can be used.

Moreover, as the charge preventing layer used in the present invention,for example, various kinds of cation charge preventing agents having acation group such as quaternary ammonium salt, pyridinium salt, andprimary to tertiary amino salts; anion charge preventing agents havingan anion group such as a sulfonic acid base, an ester sulfide base, anester phosphate base, and a phosphoric acid base; amphoteric chargepreventing agents of such as the amino acid based, and the amino estersulfide based; nonion charge preventing agents of such as the aminoalcohol based, the glycerol based, and the polyethylene glycol based;polymer type charge preventing agents with the above-mentioned chargepreventing agents provided with a high molecular weight; those formed asa film by adding a charge preventing agent such as a monomer or anoligonomer having a tertiary amino group or a quaternary ammonium groupand to be polymerized by the ionizing radiation, such as N,N-dialkylamino alkyl(meth)acrylate monomer and a quaternary compound thereto canbe presented.

The thickness of the optical functional film of the present invention isnot particularly limited, so long as it can exhibit the desired opticalcharacteristics. Ordinarily, the thickness is preferably in a range of10 μm to 200 μm, and particularly preferably in a range of 20 μm to 100μm.

Meanwhile, the haze value of the optical functional film of the presentinvention as measured according to the JIS K7105 is preferably in arange of 0% to 5%, particularly preferably in a range of 0% to 1%, andmost preferably in a range of 0% to 0.5%.

The application of the optical functional film of the present inventionis not particularly limited, and it can be used as the opticalfunctional film for various applications. As the concrete application ofthe optical functional film of the present invention, for example, anoptical compensator (for example, a viewing angle compensator), anelliptical polarizing plate, a luminance improving plate, etc. used inthe liquid crystal displays can be cited. Particular, in the presentinvention, the optical functional film can be used in the application asthe negative C-plate. When the optical functional film is used as theoptical compensator as the negative C-plate in this manner, it can befavorably used in a liquid crystal display having a liquid crystal layerwith a VA mode, an OCB mode or the like.

In addition, when the optical functional film of the present inventionis bonded to a polarizing layer, they can be used as a polarizing film.The polarizing film ordinarily comprises a polarizing layer andprotective layers formed on opposite surfaces thereof. In the presentinvention, for example, when one of the protective layers is made of theabove-mentioned optical functional film, a polarizing film having anoptical compensation function to improve the viewing anglecharacteristics of the liquid crystal display can be obtained, forexample.

Although not limited, as the above polarizing layer, an iodine basedpolarizing layer, a dye based polarizing layer using a dichromatic dye,a polyene based polarizing layer, etc. can be used, for example. Theiodine based polarizing layer and the dye based polarizing layer aregenerally produced by using polyvinyl alcohol.

The optical functional film of the present invention may be used afterbeing subjected to a drawing treatment. Although an embodiment of such adrawing treatment is not particularly limited, for example, anembodiment in which the optical functional film of the present inventionis drawn and used as a biaxial film can be given.

4. Producing Method of an Optical Functional Film

Next, a producing method of an optical functional film according to thepresent invention will be explained. The producing method of an opticalfunctional film according to the present invention is not particularlylimited, so long as it can form the optical functional layer having therandom homogeneous alignment on the above substrate. A method forcoating a composition for forming an optical functional layer preparedby dissolving the above rod-like compound on the substrate is ordinarilyused. Since the rodlike compound can be penetrated into the substratetogether with the solvent in such a method, the interaction between therodlike compound and the material constituting the substrate can bestrengthen, so that the rodlike compound is likely to form the randomhomogeneous alignment. In the following, the producing method of anoptical functional film will be explained.

The above composition for forming an optical functional layer ordinarilycomprises the rodlike compound and the solvent, and may contain othercompound, if necessary. Note that the rodlike compound used in thecomposition for forming an optical functional layer and the substrateare identical with those explained in the above “1. Optical functionallayer” and “2. Substrate”, and thus explanation is omitted here.

The solvent used in the composition for forming an optical functionallayer is not particularly limited, so long as it can solve the rodlikecompound at a given concentration. As the solvent used in the presentinvention, for example, hydrocarbon based solvents such as benzene andhexane: ketone based solvents such as methyl ethyl ketone, methylisobutyl ketone and cyclohexanone; ether based solvents such astetrahydrofuran and 1,2-dimethoxy ethane; halogenated alkyl basedsolvents such as chloroform and dichloromethane; ester based solventssuch as methyl acetate, butyl acetate and propylene glycol monomethylether acetate; amide based solvents such as N,N-dimethyl formamide;orsulfoxide based solvents such as dimethyl sulfoxide can be presented,however, it is not limited thereto . The solvent may be a single kind ora mixture of at least two kinds.

Among the above solvents, in the present invention, a ketone basedsolvent is preferably used, and cyclohexane is particularly favorablyused.

The content of the rodlike compound in the composition for forming anoptical functional layer is not particularly limited, so long as it isin such a range as to set the viscosity of the composition for formingan optical functional layer at a desired value depending upon a coatingsystem for forming the optical functional layer on the substrate bycoating, etc. Most of all, in the present invention, the content of therodlike compound in the composition for forming an optical functionallayer is preferably in a range of 0.1 mass % to 60 mass %, particularlyin a range of 1 mass % to 50 mass %, most preferably in a range of 10mass % to 40 mass %.

A photopolymerization initiator may be included in the composition forforming an optical functional layer, if needed. Particularly when theoptical functional layer is cured by irradiation with ultraviolet rays,the photopolymerization initiator is preferably included. As thephotopolymerization initiating agent, for example, benzophenone,o-benzoyl methyl benzoate, 4,4-bis(dimethyl amine)benzophenone,4,4-bis(diethyl amine)benzophenone, α-amino-acetophenone,4,4-dichlorobenzophenone, 4-benzoyl-4-methyl diphenyl ketone, dibenzylketone, fluorenone, 2,2-diethoxy acetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl propiophenone, p-tert-butyldichloroacetophenone, thioxantone, 2-methyl thioxantone,2-chlorothioxantone, 2-isopropyl thioxantone, diethyl thioxantone,benzyl dimethyl ketal, benzyl methoxy ethyl acetal, benzoin methylether, benzoin butyl ether, anthraquinone, 2-tert-butyl anthraquinone,2-amyl anthraquinone, β-chloranthraquinone, anthrone, benzanthrone,dibenzsuberone, methylene anthrone, 4-azidobenzyl acetophenone,2,6-bis(p-azidobenzylidene)cyclohexane,2,6-bis(p-azidobenzylidene)-4-methyl cyclohexanone,2-phenyl-1,2-butadion-2-(o-methoxy carbonyl)oxime, 1-phenyl-propanedion-2-(o-ethoxy carbonyl)oxime, 1,3-diphenyl-propane trion-2-(o-ethoxycarbonyl)oxime, 1-phenyl 3-ethoxy-propane trion-2-(o-benzoyl)oxime,Michler's ketone, 2-methyl-1[4-(methyl thio)phenyl]-2-morpholinopropane-1-on, 2-benzyl-2-dimethyl amino-1-(4-morpholinophenyl)-butanone, naphthalene sulfonyl chloride, quinoline sulfonylchloride, n-phenyl thioacrydone, 4,4-azo bis isobuthyronitrile, diphenyldisulfide, benzthiazol disulfide, triphenyl phosphine, camphor quinone,N1717 produced by Asahi Denka Co., Ltd., carbon tetrabromate, tribromophenyl sulfone, benzoin peroxide, eosin, or a combination of a photoreducing pigment such as a methylene blue and a reducing agent such asascorbic acid and triethanol amine can be presented as an example. Inthe present invention, these photo polymerization initiating agents canbe used only by one kind or as a combination of two or more kinds.

Furthermore, in the case of using the photo polymerization initiatingagent, a photo polymerization initiating auxiliary agent can be used incombination. As such a photo polymerization initiating auxiliary agent,tertiary amines such as triethanol amine, and methyl diethanol amine;benzoic acid derivatives such as 2-dimethyl aminoethyl benzoic acid and4-dimethyl amide ethyl benzoate, or the like can be presented, however,it is not limited thereto.

In the composition for forming an optical functional layer of thepresent invention, the following compounds may be added in the range notto deteriorate the purpose of the present invention.

As the compound to be added, for example, polyester (meth)acrylateobtained by reacting (meth)acrylic acid with a polyester prepolymerobtained by condensation of a polyhydric alcohol and a monobasic acid ora polybasic acid; polyurethane(meth)acrylate obtained by reacting apolyol group and a compound having two isocyanate groups, and reactingthe reaction product with (meth)acrylic acid; a photo polymerizablecompound such as epoxy(meth)acrylate obtained by reacting (meth)acrylicacid with epoxy resins such as a bisphenol A type epoxy resin, abisphenol F type epoxy resin, a novolak type epoxy resin, polycarboxylicacid glycidyl ester, polyol glycidyl ether, an aliphatic or alicyclicepoxy resin, an amino group epoxy resin, a triphenol methane type epoxyresin, and a dihydroxy benzene type epoxy resin; or a photopolymerizable liquid crystalline compound having an acrylic group or amethacrylic group can be presented. The addition amount of thesecompounds with respect to the composition for forming an opticalfunctional layer can be determined in the range not to deteriorate thepurpose of the present invention. Since the compounds mentioned aboveare added, the mechanical strength of the optical functional layer canbe improved so that the stability may be improved.

Other compound than the above may be included in the composition forforming an optical functional layer, if needed. Other compound, whichdepends upon the application of the optical functional film of thepresent invention, etc., is not particularly limited, so long as it doesnot damage the optical characteristics of the optical functional layerof the present invention.

As the coating method for coating the composition for forming an opticalfunctional layer onto the alignment layer is not particularly limited aslong as it is a method capable of achieving a desired flatness. As themethod, for example, the gravure coating method, the reverse coatingmethod, the knife coating method, the dip coating method, the spraycoating method, the air knife coating method, the spin coating method,the roll coating method, the printing method, the dipping and pulling upmethod, the curtain coating method, the die coating method, the castingmethod, the bar coating method, the extrusion coating method, or the Etype applying method can be presented, but they are not limited thereto.

The thickness of the coated film of the composition for forming anoptical functional layer is not particularly limited as long as it is inthe range capable of achieving a desired flatness. In general, it is inthe range of 0.1 μm to 50 μm; it is more preferably in the range of 0.5μm to 30 μm; and it is particularly preferably in the range of 0.5 μm to10 μm. In the case the thickness of the coated film of the compositionfor forming an optical functional layer is thinner than theabove-mentioned range, the flatness of the optical functional layer tobe formed may be deteriorated. Moreover, in the case the thickness isthicker than the above-mentioned range, due to the increase of the dryload of the solvent, the productivity may be lowered.

As the method for drying the coated film of the composition for formingan optical functional layer, a commonly used drying method such as theheat drying method, the pressure reducing drying method, and the gapdrying method can be used. Moreover, the drying method in the presentinvention is not limited to a single method. For example, a plurality ofdrying methods may be adopted by an embodiment such as of changing thedrying methods successively according to the residual solvent amount.

In the case of using a polymerizable material as the rodlike compound,the method for polymerizing the polymerizable material can be determinedoptionally according to the kind of the polymerizable functional groupof the polymerizable material. In particular, in the present invention,a method of curing the material by the active radiation is preferable.The active radiation is not particularly limited as long as it is aradiation capable of polymerizing the polymerizable material. Ingeneral, it is preferable to use an ultraviolet ray or a visible lightbeam in terms of the device convenience, or the like. In particular, itis preferable to use an irradiation beam having a 150 nm to 500 nmwavelength, more preferably 250 nm to 450 nm, and further preferably 300nm to 400 nm.

As the light source for the irradiation beam, for example a low pressuremercury lamp (a sterilizing lamp, a fluorescent chemical lamp, a blacklight), a high pressure discharge lamp (a high pressure mercury lamp, ametal halide lamp), or a short arc discharge lamp (a ultra high pressuremercury lamp, a xenon lamp, a mercury xenon lamp) can be presented. Inparticular, use of such as the metal halide lamp, the xenon lamp, or thehigh pressure mercury lamp can be recommended. Moreover, the irradiationcan be carried out while optionally adjusting the irradiation intensityaccording to such as the content of the photo polymerization initiatingagent.

B. Retardation Film

Next, the retardation film of the present invention will be explained.The retardation films of the present invention can be broadly classifiedinto two embodiments according to forms thereof. Therefore, theretardation film of the present invention will be explained below withrespect to each of the forms successively.

B-1: Retardation Film According to the First Embodiment

To begin with, the retardation film of the first embodiment of thepresent invention will be explained. The retardation film of thisembodiment is characterized by using the optical functional filmdescribed in the above section “A. Optical functional film” and by theretardation in the thickness direction (Rth) of the optical functionalfilm being in a range of 50 nm to 400 nm.

Since the retardation in the thickness direction (Rth) is in the aboverange according to this embodiment, the retardation film suitable forimproving the viewing angle characteristics of the liquid crystaldisplay of the VA (Vertical Alignment) system can be obtained from theoptical functional film of the present invention in combination with anA plate.

In this embodiment, the Rth is more preferably in a range of 100 nm to300 nm.

The in-plane retardation (Re) of the retardation film of this embodimentis preferably in a range of 0 nm to 5 nm. This is because, when thein-plane retardation (Re) is in the above range, the retardation film ofthis embodiment can be used as the retardation film suitable forimproving the viewing angle characteristics of the liquid crystaldisplay of the VA (Vertical Alignment) system.

The in-plane retardation (Re) value may depend upon the wavelength. Forexample, an embodiment suffices, in which the Re value is greater on thelonger wavelength side than on the shorter wavelength side, or anembodiment also suffices, in which the Re value is greater on theshorter wavelength side than on the longer wavelength side. Since the Revalue has such wavelength dependency, when the retardation film of thisembodiment is used for improving the viewing angle characteristics ofthe liquid crystal display, for example, the viewing anglecharacteristics of the liquid crystal display element can be improvedover the entire visible light zone.

Further, in this embodiment, the Re is preferable in a range of 0 nm to3 nm, more preferably in a range of 0 nm to 1 nm.

Note that the optical functional film used in this embodiment is thesame as described in the above section “A. Optical functional film”, andthus explanation is omitted here.

Further, the producing method of the retardation film of this embodimentis not particularly limited, so long as the above opticalcharacteristics can be exhibited. For example, the retardation film canbe produced by the method described in the producing method of anoptical functional film of the above “A. Optical functional film”.

B-2. Retardation Film of the Second Embodiment

Next, the retardation film of the second embodiment of the presentinvention will be explained. The retardation film of this embodimentcomprises a substrate having the property as the A plate or the B plateand the property as the negative C-plate, and a retardation layercontaining the rodlike compound, wherein the retardation layer is formeddirectly on the substrate, and the rodlike compound forms the randomhomogeneous alignment in the retardation layer.

Next, the retardation film of this embodiment will be explained withreference to the drawings. FIG. 3 is a schematically perspective viewshowing an example of the retardation film of this embodiment. As shownin FIG. 3, the retardation film 20 of this embodiment comprises asubstrate 21 and a retardation layer 22 formed directly on the substrate21. In the retardation film 20 of this embodiment, the substrate 21 hasthe property as the A plate or the B plate and the property as thenegative C-plate. Further, the retardation layer 22 contains the rodlikecompound 23 forming the random homogeneous alignment. As shown in FIG.3, the retardation film 20 of this embodiment has the configuration thatthe retardation layer 22 is formed directly on the substrate 21, and theretardation film does not have an alignment layer as an indispensableconstituent element in the conventional retardation film.

Since the retardation layer is formed directly on the substrate in theretardation film of this embodiment as shown in FIG. 3, the substrateand the retardation layer can be firmly adhered. Therefore, theretardation film has a merit of excellent adhesion stability. Further,with such improvement in the adhesion property, the retardation film hasalso merits, for example, that the alkaline resistance and reworkabilityare improved.

Here, the “formed directly” means that the substrate and the retardationlayer are formed to be brought into direct contact with each otherwithout intervention of other layer such as an alignment layer betweenthe substrate and the retardation layer, for example.

It is considered that the adhesion force between the substrate and theretardation layer is improved by forming the latter directly on theformer by the following mechanism. That is, since the formation of theretardation layer directly on the substrate allows the rod-likemolecules contained in the retardation layer to penetrate into thesubstrate from the surface thereof, there is no clear interface at abonding portion between the substrate and the retardation layer, and thebonding portion is in a “mixed” state of them. Thus, it is consideredthat the adhesion property is conspicuously improved owing to this ascompared with the bonding through the conventional interfaceinteraction.

In addition, the conventional retardation film with the alignment layerhad the problem that light underwent multiple reflections in theinterface between the alignment layer and the retardation layer and inthe interface between the alignment layer and the substrate to causeinterference fringes. However, according to the optical functional filmof this embodiment, there is no clear interface, because the film has noalignment layer and the bonding portion between the substrate and theretardation layer is in the “mixed” state. Therefore, the retardationfilm of this embodiment has the merits that the multiple reflections donot occur and the deterioration in quality does not occur owing to theinterference fringes.

The substrate used in this embodiment has the feature that it has theproperty as the A plate or the B plate. The property as the A plate inthis embodiment concretely means that the in-plane retardation (Re) ofthe substrate is not less than 30 nm. Here, the in-plane retardation(Re) is a value expressed by a formula: Re=(Nx−Ny)×d in which Nx and Nyare respectively the refractive index in the leading phase axisdirection (the direction with the smallest refractive index) and therefractive index in the lagging phase axis direction (the direction withthe largest refractive index) in the plane of the substrate used in thisembodiment, and “d” is the thickness (nm) of the retardation layer. Asthe in-plane retardation (Re) value in this embodiment, a value measuredby an automatic birefringence measuring instrument (manufactured by OjiScientific Instruments, Trade name: KOBRA-21ADH) is used.

The property as the B plate in this embodiment means that therelationship: Nx>Ny>Nz is satisfied among the Nx, Ny and Nz.

Further, the substrate used in this embodiment also has the feature thatit has the property as the negative C-plate. “The property as thenegative C-plate” in this embodiment concretely means that theretardation in the thickness direction (Rth) of the substrate is notless than 10 nm. Here, the retardation in the thickness direction (Rth)is a value expressed by a formula: Rth{(Nx+Ny)/2−Nz}×d in which Nx andNy are respectively the refractive index in the leading phase axisdirection (the direction with the smallest refractive index) and therefractive index in the lagging phase axis direction (the direction withthe largest refractive index) in the plane of the substrate used in thisembodiment, Nz is the refractive index in the thickness direction, and“d” is the thickness (nm) of the retardation layer. As the retardationvalue in the thickness direction (Rth) in this embodiment, a valuemeasured by the automatic birefringence measuring instrument(manufactured by Oji Scientific Instruments, Trade name: KOBRA-21ADH) isused.

Here, the random homogeneous alignment in this embodiment is identicalwith that explained in the above section “A. Optical functional film”,and thus explanation is omitted here.

The retardation film of the present invention comprises the substratehaving the property as the A plate or the B plate and the property asthe negative C-plate, and the retardation layer containing the rodlikecompound forming the random homogeneous alignment. Since the rodlikecompound forming the random homogeneous alignment makes the retardationlayer excellently exhibit the optical characteristics to function as thenegative C-plate, the retardation film of the present invention as awhole has the property as the A plate or the B plate and the property asthe negative C-plate. Since the retardation film of the presentinvention has such optical characteristics, only one retardation film ofthe present invention can accomplish the object as compared with theconventional method for improving the viewing angle dependency of theliquid crystal display by using two retardation films: the A plate orthe B plate and the negative C-plate.

FIGS. 4A and 4B are schematically sectional views showing examples ofthe conventional liquid crystal displays using an A plate and a negativeC-plate, and FIG. 4C is a schematically sectional view showing anexample of a liquid crystal display using the retardation film of thepresent invention. As shown in FIGS. 4A to 4C, since one retardationfilm 20 of the present invention (FIG. 4C) can perform the functions ofthe A plate 61 and the negative C-plate 62 used in FIGS. 4A and 4B, forexample, the liquid crystal display can be advantageously thinned.

The retardation film of this embodiment comprises the substrate and theretardation layer formed directly on the substrate. In the following,each of such components will be explained in detail.

1. Retardation Layer

First, the retardation layer constituting the retardation film of thisembodiment will be explained. The retardation layer in this embodimentis formed directly on the substrate mentioned later. The retardationlayer in this embodiment can be firmly adhered to the substrate byforming it directly on the substrate. Further, the retardation layer inthis embodiment contains the rodlike compound, which forms the randomhomogeneous alignment. The formation of the random homogeneous alignmentwith the rodlike compound in this manner can make the retardation filmof this embodiment excellently exhibit the optical characteristics tofunction as the negative C-plate. In the following, such a retardationlayer will be explained in detail.

(1) Rodlike Compound

The rodlike compound used in this embodiment will be explained. Therodlike compound used in this embodiment is not particularly limited, solong as it can form the random homogeneous alignment in the retardationlayer.

Here, the rodlike compound used in this embodiment is identical withthat explained in the above section “A. Optical functional film”, andthus explanation is omitted here.

(2) Other Compounds

The retardation layer in this embodiment may contain other compound(s)than the rodlike compound. Such other compound is not particularlylimited, so long as it does not disturb the random homogeneous alignmentof the rodlike compound. As such other compound, a photopolymerizationinitiator, a polymerization inhibitor, a leveling agent, a chiral agent,a silane coupling agent, etc. are given.

(3) Retardation Layer

The thickness of the optical functional layer in the present embodimentis not particularly limited, so long as it is in a range in whichdesired optical characteristics can be imparted upon the retardationlayer, depending upon the kind of the rodlike compound. Particularly, inthe present embodiment, the thickness of the retardation layer ispreferably in a range of 0.5 μm to 10 μm, more preferably in a range of0.5 μm to 8 μm, and particularly preferably in a range of 0.5 μm to 6μm. For, if the thickness of the retardation layer is greater than theabove range, it may be that the “in-plane alignment properties” as oneof the features of the random homogeneous alignment is damaged, so thatthe desired optical characteristics are not obtained. If the thicknessis smaller than the above range, it may also be that the targetedoptical characteristics are not obtained depending upon the kind of therodlike compound.

Here, in the retardation film of the present embodiment, when thebonding portion between the retardation layer and the substratementioned later possess the mixed region in which both of them are“mixed”, the thickness of the mixed region is not included in thethickness of the retardation layer.

From the standpoint of the “irregularity” and the “in-plane alignmentproperties” possessed by the random homogeneous alignment, as mentionedabove, the retardation (Re) of the retardation layer in the presentembodiment is preferably in the range of 0 nm to 5 nm, more preferablyin a range of 0 nm to 3 nm, and particularly preferably in a range of 0nm to 1 nm. Here, the definition and the measuring method of the Revalueare as mentioned above, and thus explanation is omitted here.

From the standpoint of the “in-plane alignment properties” possessed bythe above random homogeneous alignment, as mentioned above, theretardation in the thickness direction (Rth) of the retardation layer inthe present embodiment is preferably in the range of 50 nm to 400 nm,more preferably in a range of 100 nm to 300 nm, and particularlypreferably in a range of 100 nm to 200 nm. Here, the definition and themeasuring method of the Rth value are as mentioned above, and thusexplanation is omitted here.

From the standpoint of the “dispersibility” possessed by the aboverandom homogeneous alignment, as mentioned above, the haze of theretardation layer in the present embodiment is preferably 1% or less.Here, the definition and the measuring method of the haze are asmentioned above, and thus explanation is omitted here.

The configuration of the retardation layer in the present embodiment isnot limited to a single layer structure, but the retardation layer mayhave a configuration in which a plurality of layers is laminated. In thecase of the configuration in which the plural layers are laminated, thelayers having the same composition may be laminated, or the plurallayers having different compositions may be laminated. Further, in thecase of the configuration in which the retardation layer is composed ofthe plural layers, at least the retardation layer laminated directly onthe substrate has to possess the rodlike compound forming the randomhomogeneous alignment.

2. Substrate

Next, the substrate used in the present embodiment will be explained.The substrate used in the present embodiment has the function as an Aplate or B plate, and the function as the negative C-plate. Further, asmentioned later, since the above retardation layer is formed directly onthe substrate in the retardation film of the present embodiment, therodlike compound contained in the retardation layer forms the randomhomogeneous alignment. Therefore, the substrate used in the presentembodiment has a function as a so-called alignment film for making therodlike compound form the random homogeneous alignment. In thefollowing, the substrate used in the present embodiment will beexplained.

The reason why the substrate having the property as the A plate or the Bplate is used as the substrate in this embodiment is for affording theretardation film in this embodiment with the function as the A plate orthe B plate. On the other hand, the reason why the substrate having theproperty as the negative C-plate is used as that used in this embodimentis for affording the retardation film in this embodiment with thefunction as the negative C-plate and to make the rodlike compound takethe random homogeneous alignment in the retardation layer.

As mentioned above, the substrate in this embodiment functions as theso-called alignment film to make the rodlike compound form the randomhomogeneous alignment. If the substrate does not have the property asthe negative C-plate, the rodlike compound cannot form the randomhomogeneous alignment. Therefore, the substrate has the property as thenegative C-plate because of the latter reason.

In the present embodiment, the mechanism in which the rodlike compoundforms the random homogeneous alignment when the retardation layercontaining the rodlike compound is formed on the substrate having theproperty as the negative C-plate is not clear. But, this is consideredto be based on the following mechanism.

That is, for instance, if a case of the substrate being made of apolymer material is considered, it is thought that when the substratehas the property as the negative C-plate, the polymer materialconstituting the substrate is aligned random, without specificregularity, in the in-plane direction. It is thought that when the aboverodlike compound is applied onto the substrate having the polymermaterial aligned randomly in the in-plane direction on the surface, therodlike compound partially penetrates into the substrate, and themolecular axes are aligned along those molecular axes of the polymermaterial which are aligned randomly. It is thought that such a mechanismmakes the substrate having the negative C-plate exhibit the function asthe alignment film to form the random homogeneous alignment.

It is considered that the above substrate has the function as thealignment film for making the rodlike compound form the randomhomogeneous alignment through the above-mentioned mechanism. Therefore,the substrate used in the present embodiment must have an alignmentcontrolling power for the rodlike compound, and take a configuration inwhich that material constituting the substrate which exhibits theproperty as the negative C-plate must be present at the surface of thesubstrate. Accordingly, even if the substrate has the property as thenegative C-plate, that configuration cannot be used as the substrate inthe present embodiment, in which when the retardation layer is formed onthe substrate, the rodlike compound cannot contact that materialconstituting the substrate which has the alignment controlling power forthe above rodlike compound.

As such a substrate being unable to be used in this embodiment, forexample, mention may be made of a substrate having a configuration thata supporting body having a construction made of a polymer material aloneand having the property as the negative C-plate is laminated with aretardation layer containing an optically anisotropic material with arefractive index anisotropic property. In the substrate having such aconfiguration, the polymer material constituting the supporting body isthat material constituting the substrate which has the alignmentcontrolling power to the rodlike compound. However, when the retardationlayer is formed on the substrate, the rodlike compound cannot contactthe polymer material due to the presence of the retardation layer.Therefore, the substrate having such a configuration is not included inthe substrate, in this embodiment, even having the property as thenegative C-plate.

The substrate used in this embodiment is not particularly limited, solong as it has the property as the A plate or the B plate and theproperty as the negative C-plate. The property as the A plate of thesubstrate is not particularly limited, so long as the in-planeretardation (Re) is not less than 30 nm as mentioned above. In thisembodiment, the Re is preferably in a range of 30 nm to 250 nm, morepreferably in a range of 30 nm to 200 nm, and particularly preferably ina range of 30 nm to 150 nm. This is because, when the Re of thesubstrate used in this embodiment is in the above range, the retardationfilm of this embodiment can be provided with the excellent property asthe A plate. Note that the definition and the measuring method of theabove in-plane retardation are identical with those described above, andthus explanation is omitted here.

The property as the B plate of the substrate used in this embodiment isnot particularly limited, so long as the Nx, Ny and Nz satisfy therelationship: Nx>Ny>Nz. The retardation in the thickness direction (Rth)of the substrate is preferably in a range of 30 nm to 200 nm, morepreferably in a range of 30 nm to 170 nm, and particularly preferably ina range of 30 nm to 140 nm. Further, the in-plane retardation (Re) ofthe substrate is preferably in a range of 10 nm to 200 nm, morepreferably in a range of 10 nm to 150 nm, and particularly preferably ina range of 10 nm to 100 nm.

Here, the definitions and the measuring methods of the retardation inthe thickness direction (Rth) and the in-plane retardation (Re) areidentical with those described above, and thus explanation is omittedhere.

The property as the negative C-plate of the substrate used in thisembodiment is not particularly limited, the retardation in the thicknessdirection (Rth) is not less than 10 nm as mentioned above. In thisembodiment, the retardation in the thickness direction (Rth) ispreferably in a range of 10 nm to 250 nm, more preferably in a range of25 nm to 200 nm, and particularly preferably in a range of 40 nm to 150nm. This is because, when the Rth of the substrate used in thisembodiment is in the above range, the rodlike compound contained in theretardation layer can form the random homogeneous alignment having amore uniform quality. Note that the definition and the measuring methodof the retardation in the thickness direction (Rth) are identical withthose described above, and thus explanation is omitted here.

The transparency of the substrate used in the present embodiment may bedetermined optionally according to the transparency required to theretardation film of the present embodiment, or the like. In general, itis preferable that the transmittance in a visible light range is 80% ormore, and it is more preferably 90% or more. This is because, if thetransmittance is low, the selection ranges in the rodlike compound andthe like becomes narrow. Here, the transmittance of the substrate can bemeasured according to the JIS K7361-1 (Testing method of the total lighttransmittance of a plastic-transparent material).

The thickness of the substrate used in the present embodiment is notparticularly limited as long as necessary self supporting properties canbe obtained according to the application of the retardation film of thepresent embodiment, or the like. In the present embodiment, it ispreferably in the range of 10 μm to 188 μm; it is more preferably in therange of 20 μm to 125 μm; and it is particularly preferably in the rangeof 30 μm to 100 μm. In the case the thickness of the substrate isthinner than the above-mentioned range, the necessary self supportingproperties may not be provided to the retardation film of the presentembodiment. Moreover, in the case the thickness is thicker than theabove-mentioned range, for example, at the time of cutting process ofthe retardation film of the present embodiment, the process waste may beincreased or wear of the cutting blade may be promoted.

Here, in the retardation film of the present embodiment, in the case thebonding portion of the retardation layer and the substrate to beexplained has a mixed region with themselves “mixed”, the thickness ofthe retardation layer includes the thickness of the above-mentionedmixed region.

As the substrate used in the present embodiment, either a flexiblematerial having the flexible property or a rigid material without theflexible property can be used as long as it has desired opticalproperties, however, it is preferable to use a flexible material. Sincethe flexible material is used, the production process for theretardation film of the present embodiment can be provided as aroll-to-roll process so that an optical functional film having theexcellent productivity can be obtained.

Since materials constituting the flexible material are identical withthose described in the section “A. Optical functional film”, explanationis omitted here.

The substrate used in this embodiment is preferably subjected to adrawing treatment. This is because, when the substrate is subjected tothe drawing treatment, the rodlike compound can easily penetrate intothe substrate to attain excellent adhesion property between thesubstrate and the retardation layer, and the rodlike compound can formthe random homogeneous alignment having a more uniform quality.

The above drawing treatment is not particularly limited, and may bedetermined arbitrarily depending upon the material constituting thesubstrate, etc. As such a drawing treatment, a uniaxial drawingtreatment and a biaxial drawing treatment can be given by example.

The drawing condition in the drawing treatment is not particularlylimited, so long as the substrate can be provided with a desiredproperty as the A plate or the B plate and the property as the negativeC-plate.

The configuration of the substrate in this embodiment is not limited toa single layer configuration, but it may have a configuration in whichplural layers are laminated. When the substrate has the configuration inwhich the plural layers are laminated, the layers having the samecomposition may be laminated, or the plural layers having differentcompositions may be laminated.

As the configuration of the substrate in which the plural layers havingthe different compositions are laminated, an example in which a filmmade of a material such as triacetyl cellulose to make the rodlikecompound aligned randomly and homogeneously is laminated upon asupporting body made of a cycloolefin polymer having excellent waterpermeability can be given, for instance.

3. Retardation Film

The retardation film of this embodiment may have other layer than thesubstrate and the retardation layer mentioned above. As such otherlayer, a reflection preventing layer, an ultraviolet ray absorbinglayer, an infrared ray absorbing layer, a charge preventing layer, etc.can be given by example.

Since the reflection preventing layer, the ultraviolet ray absorbinglayer, the infrared ray absorbing layer, the charge preventing layer,etc. are identical with those described in the section “A. Opticalfunctional film”, explanation is omitted here.

The thickness of the retardation film of this embodiment is notparticularly limited, so long as it is in such a range to exhibit thedesired optical characteristics. Ordinary, it is preferably in a rangeof 20 μm to 150 μm, particularly preferably in a range of 25 μm to 130μm, and most preferably in a range of 30 μm to 110 μm.

Further, in the retardation film of this embodiment, the haze valuemeasured according to JIS K7105 is preferably in a range of 0% to 2%,particularly preferably in a range of 0% to 1.5%, and most preferably ina range of 0% to 1%.

The retardation in the thickness direction of the retardation film ofthis embodiment may be appropriately selected depending upon theapplication of this embodiment, etc., and is not particularly limited.Specifically, in this embodiment, the retardation in the thicknessdirection (Rth) is preferably in a range of 60 nm to 450 nm, morepreferably in a range of 70 nm to 400 nm, and particularly preferably ina range of 80 nm to 350 nm. This is because, when the retardation in thethickness direction (Rth) is in the above range, the retardation film ofthis embodiment can be made suitable for improving the viewing anglecharacteristics of the liquid crystal display of the VA (VerticalAlignment) system.

Further, the in-plane retardation (Re) of the retardation film of thisembodiment may be appropriately selected depending upon the applicationof the retardation film of this embodiment, etc., and is notparticularly limited. Specifically, in this embodiment, the in-planeretardation (Re) is preferably in a range of 20 nm to 150 nm, morepreferably in a range of 30 nm to 130 nm, and particularly preferably ina range of 40 nm to 110 nm. When the in-plane retardation (Re) is in theabove range, the retardation film of this embodiment can be used as aretardation film suitable for improving the viewing anglecharacteristics of the liquid crystal display of the VA (VerticalAlignment) system.

The in-plane retardation (Re) value may be dependent upon thewavelengths. For example, the value may be greater on the longerwavelength side than on the shorter wavelength side, or the value may begreater on the shorter wavelength side than on the longer wavelengthside. When the in-plane retardation (Re) value has such wavelengthdependency, the viewing angle characteristics of the liquid crystaldisplay can be improved over the entire visible light zone.

The application of the retardation film of this embodiment is notparticularly limited. For example, an optical compensator (for example,a viewing angle compensator), an elliptical polarizing plate, aluminance improving plate, etc. used in the liquid crystal display canbe cited. In particular, the retardation film of this embodiment can befavorably used as the optical compensator for improving the viewingangle dependency of the liquid crystal display. Further, since theretardation film of this embodiment has the property as the A plate orthe B plate and the property as the negative C-plate, it can be usedmost favorably as the optical compensator for the liquid crystal displayof the VA system.

A mode in which the retardation film of this embodiment is used as theoptical compensator of the liquid crystal display of the VA system isnot particularly limited, so long as desired viewing anglecharacteristics are obtained. The mode in which the retardation film ofthis embodiment is used as the optical compensator of the liquid crystaldisplay of the VA system will be concretely explained with reference tothe drawings. FIG. 5 give schematic views illustrating modes in whichthe retardation film of this embodiment is used as the opticalcompensator of the liquid crystal display of the VA system. FIG. 5A is aschematically sectional view showing an example of a general liquidcrystal display of the VA system without use of the retardation film ofthis embodiment. As shown in FIG. 5A, the general liquid crystal displayhas a configuration in which a liquid crystal cell 104 is sandwiched bytwo polarizing plates 30. The polarizing plate 30 takes a form in whichfilms for protecting a polarizing plate 51 are laminated on oppositefaces of the polarizer 52.

FIG. 5B is a schematically sectional view showing an example of a liquidcrystal display using the retardation film of this embodiment. As shownin FIG. 5B, an example in which the retardation film 20 of thisembodiment is laminated between a liquid crystal cell 104 and apolarizing plate 30 on a back light side can be given as a mode in whichthe retardation film of this embodiment is used as an opticalcompensator. This mode has the merit that parts having been used in theconventional liquid crystal display can be used as they are.

FIG. 5C is a schematically sectional view showing other example of aliquid crystal display using the retardation film of this embodiment. Asshown in FIG. 5C, an example in which the retardation film 20 of thisembodiment is used in place of the film for protecting a polarizingplate constituting the polarizing plate 31 on a back light side can begiven as a mode in which the retardation film 20 of this embodiment isused as an optical compensator. According to such an example, since theretardation film of this embodiment can perform the function as theoptical compensator for improving the viewing angle dependency and thefunction as the film for protecting a polarizing plate, the liquidcrystal display can be further thinned.

Further, the retardation film of this embodiment can be used for anapplication as the polarizing film by bonding it to a polarizing layer.Although the polarizing film ordinarily comprises a polarizing layer andprotective layers formed on opposite faces thereof. Meanwhile, accordingto this embodiment, when the above-mentioned retardation film isemployed as the protective layer on one of the faces, for example, thepolarizing film having the optically compensating function can beobtained for improving the viewing angle characteristics of the liquidcrystal display, for example.

Although not limited, as the above polarizing layer, an iodine basedpolarizing layer, a dye based polarizing layer using a dichromatic dye,a polyene based polarizing layer, etc. can be used, for example. Theiodine based polarizing layer and the dye based polarizing layer aregenerally produced by using polyvinyl alcohol.

4. Producing Method of the Retardation Film

Next, a producing method of the retardation film of this embodiment willbe explained. The producing method of the retardation film of thisembodiment is not particularly limited, so long as it can form theretardation layer having the random homogeneous alignment on thesubstrate. Ordinarily, a method is used, which applies a retardationlayer-forming composition prepared by dissolving the rodlike compound ina solvent onto the substrate. Since the rodlike compound can beimpregnated into the substrate together with the solvent by such amethod, the interaction between the rodlike compound and a materialconstituting the substrate can be strengthened, so that the randomhomogeneous alignment of the rodlike compound is easily formed. In thefollowing, the producing method of such a retardation film will beexplained.

The retardation layer-forming composition ordinarily comprises therodlike compound and the solvent, and may contain other compound, ifnecessary. Note that the rodlike compound used in the retardationlayer-forming composition and the substrate are identical with thoseexplained in the sections “1. Retardation layer” and “2. Substrate”, andthus explanation is omitted here.

The solvent used in the retardation layer-forming composition is notparticularly limited, so long as it can dissolve the rodlike compound ata desired concentration, and does not erode the substrate.

Here, as the solvent used in this embodiment, those identical with thesolvents explained to be employed in the composition for forming anoptical functional layer in the section “A. Optical functional film” canbe used, and thus explanation is omitted.

The content of the rodlike compound in the retardation layer-formingcomposition is not limited, so long as it is in such a range as to setthe viscosity of the retardation layer-forming composition at a desiredvalue depending upon the coating method for forming the retardationlayer on the substrate by coating, etc. Especially, in this embodiment,the content of the rodlike compound in the retardation layer-formingcomposition is preferably in a range of 10 mass % to 30 mass %,particularly preferably in a range of 10 mass % to 25 mass %, and mostpreferably in a range of 10 mass % to 20 mass %.

A photopolymerization initiator may be included in the retardationlayer-forming composition, if needed. Particularly when the retardationlayer is cured by irradiation with ultraviolet rays, thephotopolymerization initiator is preferably included. Further, when thephotopolymerization initiator is used, a photopolymerization initiatorancillary agent can be used in combination.

Here, as the photopolymerization initiator and the photopolymerizationinitiator ancillary agent to be used in the present invention, thoseidentical with what are explained as the photopolymerization initiatorand the photopolymerization initiator ancillary agent to be used in thecomposition for forming an optical functional layer in the section “A.Optical functional film” can be used, and thus explanation is omittedhere.

In the retardation layer-forming composition, the following compoundsmay be added in the range not to deteriorate the purpose of the presentembodiment. As the compound to be added, for example, polyester(meth)acrylate obtained by reacting (meth)acrylic acid with a polyesterprepolymer obtained by condensation of a polyhydric alcohol and amonobasic acid or a polybasic acid; polyurethane(meth)acrylate obtainedby reacting a polyol group and a compound having two isocyanate groups,and reacting the reaction product with (meth)acrylic acid; a photopolymerizable compound such as epoxy(meth)acrylate obtained by reacting(meth)acrylic acid with epoxy resins such as a bisphenol A type epoxyresin, a bisphenol F type epoxy resin, a novolak type epoxy resin,polycarboxylic acid glycidyl ester, polyol glycidyl ether, an aliphaticor alicyclic epoxy resin, an amino group epoxy resin, a triphenolmethane type epoxy resin, and a dihydroxy benzene type epoxy resin; or aphoto polymerizable liquid crystalline compound having an acrylic groupor a methacrylic group can be presented. The addition amount of thesecompounds with respect to the retardation layer-forming composition canbe determined in the range not to deteriorate the purpose of the presentembodiment. Since the compounds mentioned above are added, themechanical strength of the retardation layer to be formed using theretardation layer-forming composition of the present invention can beimproved so that the stability may be improved.

The coating method for coating the retardation layer-forming compositiononto the alignment layer is not particularly limited, so long as it canaccomplish a desired flatness.

Here, since the coating method used in this method is identical withthat explained as the method for coating the composition for forming anoptical functional layer in the section “A. Optical functional film”,explanation is omitted.

The thickness of the coated film of the retardation layer-formingcomposition is not particularly limited as long as it is in the rangecapable of achieving a desired flatness. In general, it is in the rangeof 0.1 μm to 50 μm; it is more preferably in the range of 0.5 μm to 30μm; and it is particularly preferably in the range of 0.5 μm to 10 μm.In the case the thickness of the coated film of the retardationlayer-forming composition is thinner than the above-mentioned range, theflatness of the retardation layer may be deteriorated. Moreover, in thecase the thickness is thicker than the above-mentioned range, due to theincrease of the dry load of the solvent, the productivity may belowered.

Since the method for drying the coated film of the retardationlayer-forming composition is identical with that explained as thecoating method for drying the coated film of the optical functionlayer-forming composition in the section “A. Optical functional film”,explanation is omitted here.

In the case of using a polymerizable material as the rodlike compound,the method for polymerizing the polymerizable material can be determinedoptionally according to the kind of the polymerizable functional groupof the polymerizable material. In particular, in the present embodiment,a method of curing the material by the active radiation is preferable.The active radiation is not particularly limited as long as it is aradiation capable of polymerizing the polymerizable material. In generalit is preferable to use a ultraviolet ray or a visible light beam interms of the device convenience, or the like. In particular, it ispreferable to use an irradiation beam having a 150 nm to 500 nmwavelength, more preferably 250 nm to 450 nm, and further preferably 300nm to 400 nm.

A light source of the irradiation light is identical with that describedin the section “A. Optical functional film”, and thus explanation isomitted here.

C. Composition for Forming an Optical Functional Layer

Next, the composition for forming an optical functional layer of thepresent invention will be explained. The composition for forming anoptical functional layer of the present invention is characterized inthat it comprises the rodlike compound and a mixed solvent composed ofan alcoholic solvent and another organic solvent, and the content of thealcoholic solvent in the mixed solvent is in a range of 5 mass % to 20mass %.

According to the present invention, since the alcoholic solvent iscontained in the mixed solvent in the above range, the opticalfunctional layer having excellent transparency can be obtained free fromclouding, when the optical functional layer is formed by using thecomposition for forming an optical functional layer of the presentinvention.

A mechanism by which, when the alcoholic solvent is contained in themixed solvent in the above range in the composition for forming anoptical functional layer of the present invention, the clouding issuppressed is not clear, but it is considered to be based on thefollowing mechanism. That is, since the rodlike compound contained inthe composition for forming an optical functional layer of the presentinvention is insoluble in the alcoholic solvent, the presence of thealcoholic solvent in the mixed solvent can promote the in-planealignment of the rod-like compound, when the optical functional layer isformed by using the composition for forming an optical functional layerof the present invention. It is considered that for such a reason, thepoor alignment of the rodlike compound can be suppressed, andconsequently the optical functional layer can be prevented from beingclouded.

In the present invention, the content of the alcoholic solvent in themixed solvent is specified to be in the range of 5 mass % to 20 mass %.The reason why it is specified to be in this range is as follows. Thatis, if the content of the alcoholic solvent is less than the aboverange, the optical functional layer can be clouded, when the opticalfunctional layer is formed by using the composition for forming anoptical functional layer of the present invention. On the other hand, ifthe content of the alcoholic solvent is more than the above range, therodlike compound mentioned later may not be dissolved at a desiredconcentration in the composition for forming an optical functional layerof the present invention.

Meanwhile, the content of the alcoholic solvent in the mixed solvent inthe present invention can be measured by gas chromatography. As to themeasuring condition of such a gas chromatography, for instance, thefollowing condition can be given by example.

-   (1) Measuring apparatus: Shimadzu Corporation-   (2) Detector: FID-   (3) Column: SBS-200 3 m-   (4) Column temperature: 100° C.,-   (5) Injection temperature: 150° C.,-   (6) Carrier gas: He 150 kPa-   (7) Hydrogen pressure: 60 kPa-   (8) Air pressure: 50 kPa

The composition for forming an optical functional layer of the presentinvention is preferably used to form the optical functional layer inwhich the rodlike compound forms the random homogeneous alignment. Sincethe optical functional layer in which the rodlike compound forms therandom homogeneous alignment excellently exhibits the opticalcharacteristics to function the negative C-plate, the optical functionallayer which excellently exhibits the optical characteristics can beformed without using the alignment film. Further, since the alignmentfilm is unnecessary, when the optical functional layer is formeddirectly on the substrate by using the composition for forming anoptical functional layer of the present invention, the opticalfunctional film having an excellent adhesion property between thesubstrate and the optical functional layer can be obtained.

The random homogeneous alignment is that one of alignment forms of therodlike compound which gives the optical characteristics as the negativeC-plate to the optical functional layer formed by using the compositionfor forming an optical functional layer of the present invention. Ingeneral, the alignment form of the rodlike compound to exhibit theoptical characteristics as the negative C-plate has been formerly thathaving the cholesterolic structure, but the random homogeneous alignmentis characterized by having no cholesterolic structure.

Here, since the random homogeneous alignment is identical with thatexplained in the section “A. Optical functional film”, explanation isomitted here.

The composition for forming an optical functional layer of the presentinvention comprises the rodlike compound and the mixed solvent composedof the alcoholic solvent and other organic solvent. In the following,each of the components of the composition for forming an opticalfunctional layer of the present invention will be explained in detail.

1. Mixed Solvent

First, the mixed solvent constituting the composition for forming anoptical functional layer of the present invention will be explained. Themixed solvent used in the present invention comprises the alcoholicsolvent and other organic solvent.

(1) Alcoholic Solvent

The alcoholic solvent used in the mixed solvent will be explained. Thealcoholic solvent used in the present invention has the function toprevent the optical functional layer from being clouded, when theoptical functional layer is formed by using the composition for formingan optical functional layer of the present invention.

The content of the alcoholic solvent in the mixed solvent in the presentinvention is not particularly limited, so long as it is in a range of 5mass % to 20 mass %. Particularly, the content is preferably in a rangeof 10 mass % to 20 mass % in the present invention. Here, a method forquantitatively determine the content of the alcoholic solvent isidentical with that mentioned above, and thus explanation is omittedhere.

The alcoholic solvent used in the present invention is not particularlylimited, so long as it does not erode the substrate mentioned later.Such an alcoholic solvent is not limited to one kind alone, but twokinds or more may be used in a mixed state.

The alcoholic solvent used in the present invention may be a monovalentalcohol in which the number of OH group contained in a molecule is oneor a polyvalent alcohol in which the number of OH groups is two or more.Particularly, the monovalent alcohol is preferably used.

Further, the alcoholic solvent used in the present invention may be anyof a primary alcohol, a secondary alcohol and a tertiary alcohol. Amongthem, the primary alcohol is preferably used.

Further, as the alcoholic solvent used in the present invention, mentionmay be made of an aliphatic saturated alcohol, an aliphatic unsaturatedalcohol, an alicyclic alcohol, an aromatic alcohol and a heterocyclicalcohol, for example. In the present invention, the aliphatic saturatedalcohol is preferably used.

As the aliphatic saturated alcohol, a lower aliphatic saturated alcoholis preferably used, and more concretely the number of carbonsconstituting the hydrocarbon chain is preferably in a range of 1 to 6,particularly preferably in a range of 3 to 5. As the lower aliphaticsaturated alcohol having the above number of the carbons, ones withstraight hydrocarbon chains and other with side chains can be recited,and any of the lower aliphatic saturated alcohols can be favorably usedin the present invention.

Among the alcoholic solvents, as specific examples of the alcoholicsolvents preferably used in the present invention, methanol, ethanol,N-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol,etc. can be recited. Particularly, isopropyl alcohol and N-propylalcohol are more preferably used in the present invention.

(2) Organic Solvent

Next, the organic solvent constituting the mixed solvent in the presentinvention will be explained. The organic solvent in the presentinvention has a function to solve the below-described rodlike compoundat a desired concentration. The organic solvent used in the presentinvention may be a single solvent or a mixed solvent of plural solvents.

The organic solvent used in the present invention is not particularlylimited, so long as it can dissolve the below-mentioned rodlike compoundat the desired concentration. As the organic solvent used in the presentinvention, mention may be made of hydrocarbon-based solvents such asbenzene, hexane, etc.; ketone-based solvents such as methyl ethylketone, methyl isobutyl ketone, cyclohexanone, methylcyclohexanone,etc.; ether-based solvents such as tetrahydrofuran, 1,2-dimethoxyethane,etc.; halogenated alkyl-based solvents such as chloroform,dichlorometahne, etc.; ester-based solvents such as methyl acetate,butyl acetate, propylene glycol monomethyl ether acetate, etc.;amide-based solvents such as N,N-dimethyl formamide, etc.; andsulfoxide-based solvents such as dimethylsulfoxide, etc., for example.Among them, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanoneand methyl cyclohexanone can be favorably used.

2. Rodlike Compound

Next, the rodlike compound constituting the composition for forming anoptical functional layer of the present invention will be explained. Therodlike compound used in the present invention is not particularlylimited, so long as it can give desired optical characteristics to theoptical functional layer formed by using the composition for forming anoptical functional layer of the present invention.

Here, the rod-like compound used in the present invention is identicalwith that explained in the section “A. Optical functional film”, andthus explanation is omitted here.

The content of the rodlike compound in the composition for forming anoptical functional layer of the present invention is not particularlylimited, so long as it is in such a range as to set the composition forforming an optical functional layer of the present invention at adesired viscosity, depending upon a forming method for forming theoptical functional layer by using the composition for forming an opticalfunctional layer of the present invention. Particularly, in the presentinvention, the content of the rodlike compound in the composition forforming an optical functional layer is preferably in a range of 5 mass %to 50 mass %, particularly preferably in a range of 5 mass % to 20 mass%.

Meanwhile, the content of the rodlike compound is determined by weighing2 g of the composition for forming an optical functional layer of thepresent invention into an aluminum cup, drying it at 150° C., in an ovenfor one hour, and then making a calculation based on a volatilizationweight loss.

3. Composition for Forming an Optical Functional Layer

The composition for forming an optical functional layer of the presentinvention may comprise other component than the above mixed solvent andthe above rodlike compound. As such other component, silicon-basedleveling agents such as polydimethyl siloxane, methylphenyl siloxane,organic denatured siloxane, etc.; straight-chain polymers such aspoly(alkyl acrylate), poly(alkyl vinylether), etc.; surface activeagents such as a fluorine-based/surface active agent, ahydrocarbon-based surface active agent, etc.; fluorine-based levelingagents such as tetrafluoroethylene, etc.; a photopolymerizationinitiator, etc. can be recited, for example. Particularly, when arodlike compound having a polymerizable functional group which ispolymerized by irradiation with light is used as the rodlike compound,the photopolymerization initiator is preferably contained in the presentinvention.

Here, the photopolymerization initiator used in the present invention isidentical with that described in the section “A. Optical functionalfilm”, and thus explanation is omitted here.

The content of the photopolymerization initiator is not particularlylimited, so long as it is in such a range as to enable thepolymerization of the rodlike compound within a desired time period.Ordinary, the content is preferably in a range of 1 weight part to 10weight parts, and particularly preferably in a range of 3 weight partsto 6 weight parts with respect to 100 weight parts of the rodlikecompound. If the content of the photopolymerization initiator is greaterthan the above range, there is a fear that the alignment of the rodlikecompound is disturbed in the optical functional layer formed by usingthe composition for forming an optical functional layer of the presentinvention. In addition, if the content is smaller than the above range,there is the possibility that the polymerization cannot be performedwithin the desired time period depending upon the kind of the rodlikecompound.

When the photopolymerization initiator is used, a photopolymerizationinitiation ancillary agent can be used in combination. Such aphotopolymerization initiator ancillary agent is identical with thatdescribed in the section “A. Optical functional film”, and thusexplanation is omitted here.

Further, other compound than mentioned above can be used in thecomposition for forming an optical functional layer of the presentinvention, so long as it does not damage the object of the presentinvention. Such other compound is identical with that explained in thesection “A. Optical functional film”, and thus explanation is omittedhere.

The viscosity of the composition for forming an optical functional layerof the present invention may be arbitrarily adjusted, depending upon themethod for forming the optical functional layer by using the compositionfor forming an optical functional layer of the present invention, etc.Ordinarily, the viscosity is preferably in a range of 0.5 mPa·s to 10mPa·s, more preferably in a range of 1 mPa·s to 5 mPa·s, and mostpreferably in a range of 1 mPa·s to 3 mPa·s at 25° C.

The application of the composition for forming an optical functionallayer of the present invention is not particularly limited, but it ispreferably used to form an optical functional layer for constituting anoptical functional film to be used in the liquid crystal display.Particularly, the composition is most preferably used to form theoptical functional layer in which the rodlike compound contained in thecomposition for forming an optical functional layer of the presentinvention forms the random homogeneous alignment. Details of such arandom homogeneous alignment are as mentioned above, and thusexplanation is omitted here.

The producing method the composition for forming an optical functionallayer of the present invention is not particularly limited, so long asit is a method capable of manufacturing the composition for forming anoptical functional layer having the above configuration. A method usedas an ordinary method used for producing an organic solvent-basedcomposition can be applied. As such a method, a method for dissolvingthe rodlike compound, etc. into the mixed solvent containing thealcoholic solvent in the above range at their respective predeterminedconcentrations can be given, for example.

D. Producing Method of the Optical Functional Film

Next, a producing method of the optical functional film of the presentinvention will be explained. The optical functional film-producingmethod of the present invention is characterized by using a substratehaving the property as the negative C-plate and the above compositionfor forming an optical functional layer, coating the composition forforming an optical functional layer on the substrate, and thus producingthe optical functional film comprising the substrate, and the rodlikecompound, which forms the random homogeneous alignment, formed directlyon the substrate.

According to the present invention, the optical functional film havingthe optical functional layer with excellent transparency can be producedby forming the optical functional layer with use of the abovecomposition for forming an optical functional layer containing thealcoholic solvent.

In addition, according to the present invention, the optical functionalfilm having an excellent adhesion property between the opticalfunctional layer and the substrate can be produced by forming theoptical functional layer directly on the substrate. It is consideredthat the adhesion force between the substrate and the optical functionallayer can be improved by forming the latter directly on the formerthrough the following mechanism. That is, when the optical functionallayer is formed directly on the substrate, the rodlike compoundcontained in the optical functional layer can penetrate into thesubstrate from the surface thereof. Consequently, there is no clearinterface at a bonding portion between the substrate and the opticalfunctional layer, but it is in a “mixed” state between them. Therefore,it is considered that the adhesion property is conspicuously improved ascompared with the conventional bonding caused by interface interaction.

In addition, in the case of the conventional optical functional filmwith the configuration having the alignment film, there were problemsthat light underwent the multiple reflections and interference fringesoccurred at the interface between the alignment film and the opticalfunctional layer and between the alignment film and the substrate.However, the optical functional film produced by the present inventionhas no such an alignment film, and the bonding portion between thesubstrate and the optical functional layer is in the “mixed” state, sono clear interface exists. Therefore, the optical functional film of thepresent invention has the merit that the above multiple reflections donot occur, and that it is free from the degradation in quality with theinterference fringes.

Further, according to the present invention, since the rodlike compoundforms the random homogeneous alignment in the optical functional layer,the optical functional film which excellently exhibits the opticalcharacteristics, particularly the optical characteristics to function asthe negative C-plate can be produced without using the alignment film.

The producing method of the optical functional film of the presentinvention uses the substrate and the composition for forming an opticalfunctional layer. In the following, the producing method of the opticalfunctional film according to the present invention will be explained indetail.

Note that the composition for forming an optical functional layer usedin the present invention is identical with that described in the section“A. Composition for forming an optical functional layer”, and thusexplanation is omitted here.

1. Substrate

Next, the substrate used in the present invention will be explained. Thesubstrate used in the present invention has the function as the negativeC-plate. Further, as mentioned later, since the optical functional layerobtained by the producing method of the optical functional film isformed directly on the substrate in the optical functional film of thepresent invention, the rodlike compound contained in the opticalfunctional layer forms the random homogeneous alignment. Therefore, thesubstrate used in the present invention has a function as a so-calledalignment film for making the rodlike compound form the randomhomogeneous alignment. In the following, the substrate used in thepresent invention will be explained.

The substrate used in the present invention is not particularly limited,so long as it has the property as the optically negative C-plate. Here,that “has the property as the optically negative C-plate” in the presentinvention means that the relationship: Nx=Ny>Nz is satisfied in which Nxand Ny are respectively the refractive index in arbitrary x-directionand y-direction in the plane of the substrate sheet, and Nz is therefractive index in the thickness direction.

The substrate having the property as the negative C-plate is used as thesubstrate in the present invention for the following reason. That is, asmentioned above, the substrate in the present invention functions as theso-called alignment film for making the rodlike compound form the randomhomogeneous alignment. If the substrate does not have the property asthe negative C-plate, the rodlike compound cannot form the randomhomogeneous alignment.

In the present invention, the mechanism in which the rodlike compoundforms the random homogeneous alignment when the optical functional layeris formed, by using the composition for forming an optical functionallayer, on the substrate having the property as the negative C-plate isthe same as those explained in the section “A. Optical functional film”,and thus explanation thereof is omitted here.

It is considered that the substrate has the function as the alignmentfilm for making the rodlike compound form the random homogeneousalignment through the above-mentioned mechanism. Therefore, thesubstrate used in the present invention must have an alignmentcontrolling power to the rodlike compound, and take a configuration inwhich that material constituting the substrate which exhibits theproperty as the negative C-plate must be present at the surface of thesubstrate. Accordingly, even if the substrate has the property as thenegative C-plate, that configuration cannot be used as the substrate inthe present invention, in which when the optical functional layer isformed on the substrate, the rodlike compound cannot contact thatmaterial constituting the substrate which has the alignment controllingpower to the rodlike compound.

As such a substrate being unable to be used in the present invention,for example, mention may be made of a substrate having a configurationthat a supporting body having a construction made of a polymer materialalone and having the property as the negative C-plate is laminated witha retardation layer containing an optically anisotropic material with arefractive index anisotropic property. In the substrate having such aconfiguration, the polymer material constituting the supporting body isthat material constituting the substrate which has the alignmentcontrolling power to the rodlike compound. However, when the aboveoptical functional layer is formed on the substrate, the rodlikecompound cannot contact the polymer material due to the presence of theretardation layer. Therefore, the substrate having such a configurationis not included in the substrate of the present invention, even if thesubstrate has the property as the negative C-plate.

The property of the negative C-plate of the substrate used in thepresent invention may be appropriately selected depending upon the kindof the rodlike compound used in the composition for forming an opticalfunctional layer, the optical characteristics required for the opticalfunctional film produced in the present invention, etc. Especially, inthe present invention, the retardation in the thickness direction (Rth)of the substrate is preferably in a range of 20 nm to 100 nm,particularly preferably in a range of 25 nm to 80 nm, and mostpreferably in a range of 30 nm to 60 nm in that range. This is because,when the retardation in the thickness direction (Rth) of the substrateis in the above range, the random homogeneous alignment is easily formedin the optical functional layer of the optical functional film producedby the present invention, irrespective of the kind of the rodlikecompound. Further, when the Rth of the substrate is in the above range,the rodlike compound can form the random homogeneous alignment having auniform quality.

Here, the above value in the thickness direction (Rth) is a retardationvalue represented by a formula: Rth={(Nx+Ny)/2−Nz}×d in which Nx and Nyare respectively the refractive index in the leading phase axisdirection (the direction with the smallest refractive index) and therefractive index in the lagging phase axis direction (the direction withthe largest refractive index) in the plane of the substrate used in thepresent invention, Nz is a refractive index in the thickness direction,and “d” is the thickness (nm) of the substrate. As the retardation (Rth)value in the present invention, a value measured by the KOBRA-WRmanufactured by Oji Scientific Instruments is used.

Further, from the standpoint that the optical functional layer havingthe rodlike compound which is aligned randomly and homogeneously with amore uniform quality is formed on the substrate in the presentinvention, in addition to the retardation in the thickness direction(Rth) being in the above range, the in-plane retardation (Re) ispreferably in a range of 0 nm to 300 nm, particularly preferably in arange of 0 nm to 150 nm, and most preferably in a range of 0 nm to 125nm.

Here, the above in-plane retardation Re is a value expressed by aformula: Re=(Nx−Ny)×d in which Nx and Ny are respectively the refractiveindex in the leading phase axis direction (the direction with thesmallest refractive index) and the refractive index in the lagging phaseaxis direction (the direction with the largest refractive index) in theplane of the substrate used in the present invention, and “d” is thethickness (nm) of the retardation layer. As the in-plane retardation(Re) value in the present invention, a value measured at roomtemperature by the KOBRA-WR manufactured by Oji Scientific Instrumentsis used.

The transparency of the substrate used in the present invention may bedetermined optionally according to the transparency required to theoptical functional film produced in the present invention, or the like.In general, it is preferable that the transmittance in a visible lightzone is 80% or more, and it is more preferably 90% or more. This isbecause, if the transmittance is low, the selection ranges in therodlike compound and the like becomes narrow. Here, the transmittance ofthe substrate can be measured according to the JIS K7361-1 (Testingmethod of the total light transmittance of a plastic-transparentmaterial).

The thickness of the substrate used in the present invention is notparticularly limited as long as necessary self supporting properties canbe obtained according to the application of the optical functional filmproduced in the present invention, or the like. In general, it ispreferably in the range of 10 μm to 188 μm; it is more preferably in therange of 20 μm to 125 μm; and it is particularly preferably in the rangeof 30 μm to 80 μm. In the case the thickness of the substrate is thinnerthan the above-mentioned range, the necessary self supporting propertiesmay not be provided to the optical functional film of the presentinvention. Moreover, in the case the thickness is thicker than theabove-mentioned range, for example, at the time of cutting process ofthe optical functional film of the present invention, the process wastemay be increased or wear of the cutting blade may be promoted.

Further, the substrate used in the present invention is not particularlylimited, so long as it possesses the optical characteristics. Since thematerial constituting such a substrate is the same as explained in thesection “A. Optical functional film”, explanation is omitted here.

The substrate used in this invention is preferably subjected to adrawing treatment. This is because, when the substrate is subjected tothe drawing treatment, the rodlike compound can easily penetrate intothe substrate to attain excellent adhesion property between thesubstrate and the retardation layer. As a result, the rodlike compoundcan form the random homogeneous alignment having a more uniform quality.

The above drawing treatment is not particularly limited, and may bedetermined arbitrarily depending upon the material constituting thesubstrate, etc. As such a drawing treatment, a uniaxial drawingtreatment and a biaxial drawing treatment can be given by example. Amongthem, the biaxial drawing treatment is preferable as the drawingtreatment applied in the present invention.

The drawing method in the biaxial drawing treatment is not particularlylimited, so long as it can impart the desired property as the negativeC-plate to the substrate. In the present invention, any drawing methodsuch as a roller drawing method, a long-gap extension drawing method, atenter drawing method, a tubular drawing method or the like can beappropriately used. In the drawing treatment, the polymer film ispreferably heated at not less than the glass transition temperature andnot more than the melting point, for example.

The configuration of the substrate in the present invention is notlimited to a single layer configuration, but it may have a configurationin which plural layers are laminated. When the substrate has theconfiguration in which the plural layers are laminated, the layershaving the same composition may be laminated, or the plural layershaving different compositions may be laminated.

As the configuration of the substrate in which the plural layers havingthe different compositions are laminated, an example in which a filmmade of a material such as triacetyl cellulose to make the rodlikecompound aligned randomly and homogeneously is laminated upon asupporting body made of a cycloolefin polymer having excellent waterpermeability can be given, for instance.

2. Producing Method of the Optical Functional Film

Next, the producing method of the optical functional film in the presentinvention by using the composition for forming an optical functionallayer and by forming the optical functional layer on the substrate willbe explained. Meanwhile, in the optical functional film-producing methodof the present invention, the optical functional layer is formed bycoating the composition for forming an optical functional layer directlyon the substrate.

As the coating method for coating the composition for forming an opticalfunctional layer onto the substrate is not particularly limited as longas it is a method capable of achieving a desired flatness. As themethod, for example, the gravure coating method, the reverse coatingmethod, the knife coating method, the dip coating method, the spraycoating method, the air knife coating method, the spin coating method,the roll coating method, the printing method, the dipping and pulling upmethod, the curtain coating method, the die coating method, the castingmethod, the bar coating method, the extrusion coating method, or the Etype applying method can be presented, but it is not restricted thereto.

The thickness of the coated film of the composition for forming anoptical functional layer is not particularly limited as long as it is inthe range capable of achieving a desired flatness. In general, it is inthe range of 0.1 μm to 50 μm; it is more preferably in the range of 0.5μm to 30 μm; and it is particularly preferably in the range of 0.5 μm to10 μm. In the case the thickness of the coated film of the compositionfor forming an optical functional layer is thinner than theabove-mentioned range, the flatness of the optical functional layer tobe formed may be deteriorated. Moreover, in the case the thickness isthicker than the above-mentioned range, due to the increase of the dryload of the solvent, the productivity may be lowered.

As the method for drying the coated film of the composition for formingan optical functional layer, a commonly used drying method such as theheat drying method, the pressure reducing drying method, and the gapdrying method can be used. Moreover, the drying method in the presentinvention is not limited to a single method. For example, a plurality ofdrying methods may be adopted by an embodiment such as of changing thedrying methods successively according to the residual solvent amount.

In the case of using a polymerizable material as the rodlike compound,the method for polymerizing the polymerizable material can be determinedoptionally according to the kind of the polymerizable functional groupof the polymerizable material. In particular, in the present invention,a method of curing the material by the active radiation is preferable.The active radiation is not particularly limited as long as it is aradiation capable of polymerizing the polymerizable material. In generalit is preferable to use an ultraviolet ray or a visible light beam interms of the device convenience, or the like. In particular, it ispreferable to use an irradiation beam having a 150 nm to 500 nmwavelength, more preferably 250 nm to 450 nm, and further preferably 300nm to 400 nm.

As the light source for the irradiation beam, for example a low pressuremercury lamp (a sterilizing lamp, a fluorescent chemical lamp, a blacklight), a high pressure discharge lamp (a high pressure mercury lamp, ametal halide lamp), or a short arc discharge lamp (a ultra high pressuremercury lamp, a xenon lamp, a mercury xenon lamp) can be presented. Inparticular, use of such as the metal halide lamp, the xenon lamp, or thehigh pressure mercury lamp can be recommended. Moreover, the irradiationcan be carried out while optionally adjusting the irradiation intensityaccording to such as the content of the photo polymerization initiatingagent.

3. Optical Functional Film

Lastly, the optical functional film produced by the optical functionalfilm-producing method of'the present invention will be explained. Theoptical functional film produced by the present invention comprises thesubstrate and the optical functional layer formed directly on thesubstrate. In the optical functional layer, the rodlike compound formsthe random homogeneous alignment.

Since the optical functional layer is formed by using the abovecomposition for forming an optical functional layer, the opticalfunctional film produced by the present invention has excellenttransparency.

The optical functional film produced by the present invention ischaracterized by having the merit that when it is used for anapplication as an optical compensation film for the liquid crystaldisplay, less fringes or clouding occurs and high displaying quality canbe realized.

Further, the optical functional film produced by the present inventionhas the merit that since the substrate and the optical functional layercan be firmly adhered by forming the optical functional layer directlyon the substrate, the delamination or the like does not occur with lapseof time.

Furthermore, since the rodlike compound forms the random homogeneousalignment in the optical functional layer, the optical functional filmproduced by the present invention excellently exhibits the opticalcharacteristics to function as the negative C-plate.

In the following, the optical functional film produced by the opticalfunctional film-producing method of the present invention will beexplained in detail. Note that the random homogeneous alignment in thepresent invention is identical with that explained in the section “A.Optical functional film”, and thus explanation is omitted here.

The thickness of the optical functional film produced by the presentinvention is not particularly limited, so long as it is in such a rangeas to exhibit the desired optical characteristics. Ordinary, it ispreferably in a range of 30 μm to 200 μm, particularly preferably in arange of 30 μm to 150 μm, and most preferably in a range of 30 μm to 100μm.

Moreover, in the optical functional film produced by the presentinvention, the haze value measured according to JIS K7105 is preferablyin a range of 0.1% to 5%, particularly in a range of 0.1% to 1%, andmost preferably in a range of 0.1% to 0.5%.

The retardation in the thickness direction (Rth) of the opticalfunctional film produced by the present invention may be appropriatelyselected depending upon the application of the optical functional film,etc., and is not particularly limited. Especially, in the presentinvention, the retardation in the thickness direction (Rth) ispreferably in a range of 50 nm to 500 nm, more preferably in a range of100 nm to 400 nm, and particularly preferably in a range of 100 nm to400 nm. Since the retardation in the thickness direction (Rth) is in theabove range, the optical functional film produced by the presentinvention can be made suitable for improving the viewing anglecharacteristics of the liquid crystal display of the VA (VerticalAlignment) system. Here, the definition and the measuring method of theretardation in the thickness direction (Rth) are identical with thoseexplained in the section “1. Substrate”, and thus explanation is omittedhere.

In addition, the in-plane retardation (Re) of the optical functionalfilm produced by the present invention may be appropriately selecteddepending upon the application of the optical functional film, etc., andis not particularly limited. Especially, in the present invention, thein-plane retardation (Re) is preferably in a range of 0 nm to 5 nm, morepreferably in a range of 0 nm to 3 nm, and particularly preferably in arange of 0 nm to 1 nm. Since the in-plane retardation (Re) is in theabove range, the optical functional film produced by the presentinvention can be used as a retardation film suitable for improving theviewing angle characteristics of the liquid crystal display of the VA(Vertical Alignment) system.

Here, the definition and the measuring method of the in-planeretardation (Re) are identical with those explained in the section “1.Substrate”, and thus explanation is omitted here.

The above in-plane retardation (Re) value may have the wavelengthdependency. For example, a mode in which the Re value is greater on thelonger wavelength side than on the shorter wavelength side suffices, ora mode in which the Re value is greater on the shorter wavelength sidethan on the longer wavelength side suffices.

The application of the optical functional film produced by the presentinvention is not particularly limited, but it can be used as the opticalfunctional film for various applications. For example, concreteapplications of the optical functional film of the present invention arean optical compensator (for example, a viewing angle compensator), anelliptical polarizing plate, a luminance improving plate, etc. can becited. Particularly, in the present invention, the optical functionalfilm can be favorably used in an application as the negative C-plate.When the optical functional film is used as the optical compensationplate being the negative C-plate, it is favorably used in a liquidcrystal display having a liquid crystal layer of the VA mode or the OCBmode.

Further, the optical functional film of the present invention can beused as a polarizing plate by bonding it to a polarizer. The polarizingplate ordinarily comprises the polarizer and films for protecting apolarizing plate formed on opposite surfaces thereof. In the presentinvention, since the optical functional film produced by the presentinvention is used as the film for protecting a polarizing plate on oneside of the polarizing plate, the polarizing plate having opticalcompensation function for improving the viewing angle characteristics ofthe liquid crystal display can be obtained, for example.

Although not limited, as the above polarizer, an iodine based polarizer,a dye based polarizer using a dichromatic dye, a polyene basedpolarizer, etc. can be used, for example. The iodine based polarizer andthe dye based polarizer are generally produced by using polyvinylalcohol.

Furthermore, the optical functional film of the present invention may beused after being subjected to a drawing treatment. Although anembodiment of such a drawing treatment is not particularly limited, forexample, an embodiment in which the optical functional film obtained bythe present invention is drawn and used as a biaxial film can be given.

The present invention is not limited to the above-mentioned embodiments.The embodiments are examples and any one having the substantially sameconfiguration as the technological idea disclosed in the claims of thepresent invention so as to achieve the same effects is incorporated inthe technological scope of the present invention.

EXAMPLES

Hereinafter, the present invention will be explained specifically withreference to the example.

Example 1

Into cyclohexane was dissolved a compound (I) expressed by the followingformula as a rodlike compound in an amount of 20 mass %, and theresultant was coated onto a substrate made of a TAC film (manufacturedby FUJIFILM Corporation, Trade name: TF80UL) by bar coating in a coatedamount of 2.5 g/m² after drying. Subsequently, the solvent was dried offby heating at 90° C., for 4 minutes, the rodlike compound was penetratedinto the TAC film, and the rodlike compound was fixed by irradiating thecoated face with ultraviolet rays, thereby producing a retardation film.The obtained retardation film was taken as a sample, and evaluated withrespect to the following items.

1. Random Homogeneous Alignment

With respect to the produced retardation film and the TF80UL, the Rthand the Re were measured according to the parallel Nicol rotation methodby using the KOBRA-WR manufactured by Oji Scientific Instruments. TheRth and the Re of the optical functional layer were determined bysubtracting the measured Rth and Re values of the TF80UL from those ofthe retardation film, respectively. Here, Trade name: KOBRA-21ADHmanufactured by Oji Scientific Instruments was used for the abovemeasurements of the Re and Rth. Meanwhile, Trade name: NDH2000manufactured by Nippon Denshoku Industries Co., Ltd. was used for themeasurement of the above haze. Further, Trade name: UV-3100PCmanufactured by Shimazdu Corporation was used for confirming thepresence or absence of the above selective reflection wavelength. As aresult, Rth=117.9 nm, and Re=0 nm. Meanwhile, the haze was 0.2%.

In addition, it was confirmed by a UV-VIS-NIR spectrophotometer(UV-3100) manufactured by Shimazdu Corporation that the retardation filmhas no selective reflection wavelength.

2. Adhesion Property Test

In order to examine the adhesion property, a peeling test was carriedout. In the peeling test, 1 mm-square cut lines were formed on theobtained sample in a grid fashion. An adhesive tape (manufactured byNICHIBAN CO., LTD., Cellotape (registered trademark)) was bonded to aliquid crystal face, then the tape was peeled off, and observation wasmade by eyes. As a result, the adhesion degree was 100%.Adhesion degree (%)=(non-peeled portion/tape-bonded area)×100.3. Wet Heat Resistance Test-1

A sample was immersed in hot water at 90° C., for 60 minutes, and theoptical characteristics and the adhesion property were measured by theabove-mentioned methods. As a result, no change was seen in the opticalcharacteristics and the adhesion property before and after the testing.

4. Wet Heat Resistance test-2

A sample was left at rest in an environment of a humidity 95% at 80° C.,for 24 hours, and the optical characteristics and the adhesion propertywere measured by the above-mentioned methods. As a result, no change wasseen in the optical characteristics and the adhesion property before andafter the testing. Meanwhile, neither oozing nor clouding of therefractive index anisotropic material was seen after the testing.

5. Water Proof Test

A sample was immersed into pure water at room temperature (23.5° C.,)for one day, and the optical characteristics and the adhesion propertywere measured by the above-mentioned methods. As a result, no change wasseen in the optical characteristics and the adhesion property before andafter the testing.

6. Alkaline Resistance Test

A sample was immersed into an alkaline aqueous solution (1.5N aqueoussolution of sodium hydroxide) at 55° C., for 3 minutes, and washed anddried, and the optical characteristics and the adhesion property weremeasured by the above-mentioned methods. As a result, no change was seenin the optical characteristics and the adhesion property before andafter the testing. Furthermore, no coloring was seen.

Example 2

Into cyclohexane was dissolved the compound (I) having the formulamentioned above as the rodlike compound in an amount of 20 mass %, andthe resultant was coated onto a non-drawn COP (cycloolefin polymer) film(manufactured by JSR Corporation, Trade name: ARTON) by bar coating.Subsequently, the solvent was removed by heating at 50° C., for 2minutes, the photopolymerizable liquid crystalline compound was fixed byirradiating the coated face with ultraviolet rays, and the residualsolvent was removed by further heating at 90° C., for 2 minutes, therebyproducing a retardation film. The obtained retardation film was taken asa sample, and evaluated with respect to the following items.

1. Random Homogeneous Alignment

With respect to the retardation layer of the produced retardation film,the Re, the presence or absence of the selective reflection wavelength,the Rth and the haze were evaluated. The measurements were carried outwith respect to the entire retardation film and the non-drawn COP(cycloolefin polymer) film (manufactured by JSR Corporation, trade name:ARTON), respectively, and the measured values of the latter weresubtracted from those of the former. Here, Trade name: KOBRA-21ADHmanufactured by Oji Scientific Instruments was used for the measurementof the above Re and Rth. Meanwhile, Trade name: NDH2000 manufactured byNippon Denshoku Industries Co., Ltd. was used for the measurement of theabove haze. Further, Trade name: UV-3100PC manufactured by ShimazduCorporation was used for confirming the presence or absence of the aboveselective reflection wavelength. As a result, the retardation layer ofthe produced retardation film had Rth=106.6 nm, Re=2.9 nm, thehaze=0.04%, and no selective reflection wavelength. Thereby, in theretardation layer of the produced retardation film, it was confirmedthat the above photopolymerizable liquid crystalline compound wasaligned randomly and homogeneously.

2. Optical Characteristics

The retardation of a sample was measured by the automatic birefringencemeasuring instrument (manufactured by Oji Scientific Instruments, Tradename: KOBRA-21ADH). Measuring light was introduced vertically orobliquely to a surface of the sample, and the anisotropic property toincrease the retardation of the substrate film was confirmed based on achart of the optical retardation and the incident angle of the measuringlight.

3. Haze

In order to examine the transparency of a sample, the haze value wasmeasured by a turbidimeter (manufactured by Nippon Denshoku IndustriesCo., Ltd., trade name: NDH2000). The result was good with not more than0.3% at a coated amount of 3 g/m².

4. Adhesion Property Test

In order to examine the adhesion property, a peeling test was carriedout. In the peeling test, 1 mm-square cut lines were formed on theobtained sample in a grid fashion. An adhesive tape (manufactured byNICHIBAN CO., LTD., Cellotape (registered trademark)) was bonded to aliquid crystal face, then the tape was peeled off, and observation wasmade by eyes. As a result, the adhesion degree was 100%.Adhesion degree (%)=(non-peeled portion/tape-bonded area)×100.5. Wet Heat Resistance Test

A sample was immersed in hot water at 90° C., for 60 minutes, and theoptical characteristics and the adhesion property were measured by theabove-mentioned methods. As a result, no change was seen in the opticalcharacteristics and the adhesion property before and after the testing.

6. Water Proof Test

A sample was immersed into pure water at room temperature (23.5° C.,)for one day, and the optical characteristics and the adhesion propertywere measured by the above-mentioned methods. As a result, no change wasseen in the optical characteristics and the adhesion property before andafter the testing.

Example 3

Into cyclohexane was dissolved a photopolymerizable liquid crystallinecompound expressed by the above formula (I) as the rodlike compound inan amount of 20 mass %, and the resultant was coated on a uniaxiallydrawn COP (cycloolefin polymer) film (manufactured by JSR Corporation,trade name: ARTON) by bar coating. Subsequently, the solvent was removedby heating at 50° C., for 2 minutes, the above photopolymerizable liquidcrystalline compound was fixed by irradiating the coated face withultraviolet rays, and the residual solvent was removed by furtherheating at 90° C., for 2 minutes, thereby producing a retardation film.The obtained retardation film was taken as a sample, and evaluated withrespect to the following items.

1. Random Homogeneous Alignment

With respect to the retardation layer of the produced retardation film,the Re, the presence or absence of the selective reflection wavelength,the Rth and the haze were evaluated. The measurements were carried outwith respect to the entire retardation film and the above uniaxialdrawing COP (cycloolefin polymer) film (manufactured by JSR Corporation,trade name: ARTON), respectively, and the measured values of the latterwere subtracted from those of the former. Here, Trade name: KOBRA-21ADHmanufactured by Oji Scientific Instruments was used for the measurementof the above Re and Rth. Meanwhile, Trade name: NDH2000 manufactured byNippon Denshoku Industries Co., Ltd. was used for the measurement of theabove haze. Further, Trade name: UV-3100PC manufactured by ShimazduCorporation was used for confirming the presence or absence of the aboveselective reflection wavelength. As a result, the retardation layer ofthe produced retardation film had Re=2.9 nm, Rth=106.6 nm, thehaze=0.04%, and no selective reflection wavelength. Thereby, in theretardation layer of the produced retardation film, it was confirmedthat the above photopolymerizable liquid crystalline compound wasaligned randomly and homogeneously.

2. Optical Characteristics

The retardation of a sample was measured by the automatic birefringencemeasuring instrument (manufactured by Oji Scientific Instruments, Tradename: KOBRA-21ADH). Measuring light was introduced vertically orobliquely to a surface of the sample, and the anisotropic property toincrease the retardation of the substrata film was confirmed based on achart of the optical retardation and the incident angle of the measuringlight. Moreover, the three-dimensional refractive index was measured bythe same measurement device. The results are shown in the followingtable.

TABLE 1 Nx 1.59 Ny 1.55 Nz 1.533. Haze

In order to examine the transparency of a sample, the haze value wasmeasured by a turbidimeter (manufactured by Nippon Denshoku IndustriesCo., Ltd., trade name: NDH2000). The result was good with not more than0.3% at a coated amount of 3 g/m².

4. Adhesion Property Test

In order to examine the adhesion property, a peeling test was carriedout. In the peeling test, 1mm-square cut lines were formed on theobtained sample in a grid fashion. An adhesive tape (manufactured byNICHIBAN CO., LTD., Cellotape (registered trademark)) was bonded to aliquid crystal face, then the tape was peeled off, and observation wasmade by eyes. As a result, the adhesion degree was 100%.Adhesion degree (%)=(non-peeled portion/tape-bonded area)×100.5. Wet Heat Resistance Test

A sample was immersed in hot water at 90° C., for 60 minutes, and theoptical characteristics and the adhesion property were measured by theabove-mentioned methods. As a result, no change was seen in the opticalcharacteristics and the adhesion property before and after the testing.

6. Water Proof Test

A sample was immersed into pure water at room temperature (23.5° C.,)for one day, and the optical characteristics and the adhesion propertywere measured by the above-mentioned methods. As a result, no change wasseen in the optical characteristics and the adhesion property before andafter the testing.

Example 4

The compound expressed by the above formula (I) was used as /nematicliquid crystals, and dissolved in a mixed solvent of anone: isopropylalcohol=9:1 by mass ratio in an amount of 20 mass %. A composition forforming an optical functional layer was prepared with aphotopolymerization initiator (Irgacure 907, manufactured by Ciba-GeigyJapan Limited) adjusted in the resultant at 1 mass % relative to themass of the nematic liquid crystals.

That ink composition was coated on a substrate of a triacetyl cellulose(TAC) film having a thickness of 80 μm by bar coating, which was driedat 50° C., in an oven for 2 minutes and thereafter subjected to curingby irradiation with ultraviolet rays at 100 mJ/cm² under nitrogenatmosphere, thereby forming an optical functional layer and producing anoptical (compensation) film.

Example 5

An optical (compensation) film was produced by the same method as inExample 4 except that a mixed solution of anone: n-propyl alcohol=9:1 bymass ratio was used.

Example 6

An optical (compensation) film was produced by the same method as inExample 4 except that a mixed solution of anone: n-propyl alcohol=8:2 bymass ratio was used.

Comparative Example 1

An optical (compensation) film was produced by the same method as inExample 4 except that a mixed solution of anone: isopropyl alcohol=7:3by mass ratio was used.

Comparative Example 2

An optical (compensation) film was produced by the same method as inExample 4 except that a mixed solution of anone: n-propyl alcohol=7:3 bymass ratio was used.

Comparative Example 3

The same nematic liquid crystals as used in Example 4 were dissolved inan amount of 20 mass % into a solvent consisting of anone alone. Acomposition for forming an optical functional layer was prepared withthe photopolymerization initiator (Irgacure 907, manufactured byCiba-Geigy Japan Limited) adjusted in the resultant at 1 mass % relativeto the mass of the nematic liquid crystals. Then, an optical(compensation) film was produced in the same manner as in Example 1.

(Evaluations)

(1) Haze and Total Light Transmission (%)

The hazes and the total light transmissions of the optical(compensation) films produced in the above Examples and ComparativeExamples were measured according to JIS K7361.

(2) Fringe and Clouding in a Crossed Nicol State

With respect to the optical (compensation) films produced in theExamples 4 to 6 and Comparative Examples 1 to 3, commercially availablepolarizing plates (HCL2-5618HCS, manufactured by SANRITZ CORPORATION)were bonded on opposite sides in a crossed Nicol arrangement, theresultant was installed on a liquid crystal-backlight, and fringe andclouding degrees at front face were visually observed and evaluated in adark room. The Judging standard for evaluating the clouding degrees isas follows.

∘: Good with no clouding observed and high transparency

X: Bad with clouding observed and decreased transparency

The above evaluation results are shown in Table 2. As shown in Table 2,the optical (compensation) films in Examples were good in terms of thehaze, and the fringe and clouding in the crossed Nicol state. On theother hand, none of the optical (compensation) films in ComparativeExamples were good in terms of the haze, and the fringe and clouding inthe crossed Nicol state.

TABLE 2 TOTAL LIGHT HAZE TRANS- CLOUD- (%) MISSION (%) FRINGE INGEXAMPLE 0.34 91.8 ∘ ∘ 4 EXAMPLE 0.34 91.9 ∘ ∘ 5 EXAMPLE 0.38 91.7 ∘ ∘ 6COMPARATIVE 1.49 91.9 x x EXAMPLE 1 COMPARATIVE 0.39 91.9 x ∘ EXAMPLE 2COMPARATIVE 0.33 91.8 x x EXAMPLE 3

1. A composition for optical functional layer comprising: a rodlikecompound, and a mixed solvent containing an alcoholic solvent andanother organic solvent, wherein a content of the alcoholic solvent inthe mixed solvent is in a range of 5mass % to 20mass %, and the rodlikecompound is insoluble in the alcoholic solvent, and wherein thecomposition is used to form an optical functional layer in which therodlike compound forms a random homogeneous alignment.
 2. Thecomposition for optical functional layer set forth in claim 1, whereinthe rodlike compound has a polymerizable functional group.
 3. Thecomposition for optical functional layer set forth in claim 1, whereinthe rodlike compound is a liquid crystalline material.
 4. Thecomposition for optical functional layer set forth in claim 3, whereinthe liquid crystalline material is a material exhibiting a nematicphase.
 5. A producing method of an optical functional film, comprising:a substrate having a property as a negative C-plate, and the compositionfor optical functional layer set forth in claim 1, wherein thecomposition for optical functional layer is coated onto the substrate toproduce an optical functional film comprising the substrate, and anoptical functional layer formed directly on the substrate and containingthe rodlike compound forming a random homogeneous alignment.